# Fire and Gas Barrier Properties of Poly(styrene-co-acrylonitrile) Nanocomposites Using Polycaprolactone/Clay Nanohybrid Based-Masterbatch

Authors: S. Benali; A. Olivier; P. Brocorens; L. Bonnaud; M. Alexandre; S. Bourbigot; E. Espuche; F. Gouanve; R. Lazzaroni; Ph. Dubois
Journal: Advances in Materials Science and Engineering
 (2008)

---

## Abstract

Exfoliated nanocomposites are prepared by dispersion of poly(ε-caprolactone) (PCL) grafted montmorillonite nanohybrids used as masterbatches in poly(styrene-co-acrylonitrile) (SAN). The PCL-grafted clay nanohybrids with high inorganic content are synthesized by in situ intercalative ring-opening polymerization of ε-caprolactone between silicate layers organomodified by alkylammonium cations bearing two hydroxyl functions. The polymerization is initiated by tin alcoholate species derived from the exchange reaction of tin(II) bis(2-ethylhexanoate) with the hydroxyl groups borne by the ammonium cations that organomodified the clay. These highly filled PCL nanocomposites (25 wt% in inorganics) are dispersed as masterbatches in commercial poly(styrene-co-acrylonitrile) by melt blending. SAN-based nanocomposites containing 3 wt% of inorganics are accordingly prepared. The direct blend of SAN/organomodified clay is also prepared for sake of comparison. The clay dispersion is characterized by wide-angle X-ray diffraction (WAXD), atomic force microscopy (AFM), and solid state NMR spectroscopy measurements. The thermal properties are studied by thermogravimetric analysis. The flame retardancy and gas barrier resistance properties of nanocomposites are discussed both as a function of the clay dispersion and of the matrix/clay interaction.


---

## Body

## 1. Introduction

The research
concerning polymer nanocomposites based on organolayered silicates [1–6] highlighted
the interest of such clays not only for increasing the stiffness [4] of
these materials, but also for enhancing other properties of the polymers such
as thermal [5, 7–9], flame
retardancy [5, 10] or gas barrier resistance properties [11, 12].The possibility
of reaching a large enhancement of polymer properties lies in the obtention of
a high level of nanoparticle dissociation for an efficient separation of the
silicate layers [1]. However, the
use of classical processes for nanocomposite preparation (in situ intercalative polymerization
or melt intercalation/delamination) is often insufficient to reach a
homogeneous dispersion of these nanoparticles [1, 6].Recently, a new
two-step route to polymer/layered silicate nanocomposites characterized by a
large extent of nanoplatelet delamination has been investigated [13–16]. This
efficient process, that is, the “poly(ε-caprolactone)  (PCL)/clay nanohybrid
masterbatch” technique, consists in combining a “grafting-from” intercalative
polymerization followed by a melt delamination process. In the first step, an
organomodified clay is prepared by ion exchange of sodium cations naturally
present in montmorillonite (MMT) with an adequate amount of hydroxylated
alkylammonium cations. Then, the silicate layers are delaminated by catalyzed
ring-opening polymerization of ε-caprolactone
directly initiated from this adequately organomodified filler surface. And
finally, the resulting polyester-grafted organoclay nanohybrids are used as
masterbatches and are dispersed in commercial polymeric matrices by melt
blending. This technique has already successfully led
to a large improvement of clay dispersion within the PCL matrix [17] and a
chlorinated polyethylene matrix [15, 16]. In each case, typical properties of nanocomposites
are studied both as a function of the clay dispersion and of the matrix/clay
interactions.Poly(styrene-co-acrylonitrile)
(SAN) exhibits several interesting properties such as good mechanical and chemical
resistance, optical transparency, and ease of processing. SAN
is widely used in many
applications in the household and sanitary sectors, for packaging cosmetic products
as well as for electronic and office items. A number of studies on
nanocomposites based on an SAN matrix have been published. These studies have been mainly focused
on the organomodified clay effect [8, 10, 18, 19], acrylonitrile (AN) content
effect [19–21], or the use
of compatibilizing agent like PCL [22, 23] introduced by melt blending.
Whatever the techniques used in these different works, only intercalated
structures were evidenced by both WAXD and TEM analysis and thermal and flame
retardancy properties have more or less been improved as a function of
parameters studied. However, as
expected from the general trends in nanocomposites properties [1, 6], these
results should be enhanced by clay dispersion improvement.So, the present work focuses
on the PCL/clay nanohybrid masterbatch approach with SAN as the diluting
matrix, in order to prepare new materials with an exfoliated nanostructure.
Indeed, the miscibility between SAN and PCL [22, 23] allows to use PCL as a
compatibilizer agent between SAN and MMT. Our study is part of a larger effort, which aims at developing SAN
foams. So, it is worth rating that the present work does not aim first at
improving the mechanical properties of SAN nanocomposites but rather at studying
the relationships between the clay dispersion and the flame retardancy or barrier
gas resistance properties. In order to highlight the interest of
the PCL/clay nanohybrid masterbatch technique, a
comparison has been carried out with just a melt intercalated
SAN/organomodified clay.


## 2. Experimental Part

### 2.1. Materials

ε-caprolactone (CL, Fluka) was dried over CaH2 and distilled under reduced pressure prior to use. Tin (II)
bis(2-ethylhexanoate), also known as tin(octoate) (Sn(Oct)2), was
purchased from Fluka (Switzerland), diluted with dried toluene, and stored
under nitrogen atmosphere.Commercial SAN, Luran 358N
(with 75 wt% of styrene) was supplied by BASF (Belgium). The SAN was systematically further
stabilized by 0.05 wt% of Irganox MD1024 supplied by CIBA (Switzerland). CAPA 2402, a PCL oligomer (Mn  = 4000 g.mol−1)
was obtained from Solvay Interox (UK). Cloisite 30B (CL30B), a montmorillonite
organomodified by 23.4 wt% of methyl bis(2-hydroxyethyl)tallowalkyl ammonium
cations was supplied by Southern Clay Products (Texas, USA).


### 2.2. Characterization

Thermogravimetric analysis (TGA) was performed at a heating rate of
20°C/min from room temperature to 800°C by using an Hi-Res TGA 2950 device from TA Instruments (Del, NY, USA). Thermodegradation was determined on approximately 15 mg samples
with platinum sample pan in a 74 cm3/min helium flow.
Thermooxidation was determined in the same way in a 69 cm3/min air
flow.The morphology of the nanocomposites has been analyzed by wide-angle
X-ray diffraction (WAXD) and atomic force microscopy (AFM). WAXD patterns were
recorded between 1.65°  and 30° (by steps of 0.04°) with a Siemens D5000
diffractometer (Germany) operating with CuKα radiation (λ=1.5406 Å). For recording AFM images, the samples were cryomicrotomed at −100°C by
an Ultracut FC4E microtome from Reichert-Jung (Austria). A truncated pyramid is
cut in the sample. Ultrathin sections of the pyramid are removed, while the ~1 × 1.5 mm2 top surface of the pyramid is imaged with AFM. The AFM
images were recorded in tapping mode (TM) with a Nanoscope IIIa microscope from
Veeco Instruments (USA). Both
height and phase images of 512×512 data points were recorded in ambient
atmosphere, at room temperature, using silicon probes with a spring constant of
24–52 N/m, a
resonance frequency in the 264–339 kHz range,
and a typical radius of curvature of 10–15 nm. The
selected AFM images are representative of the morphology of the whole sample,
as based on the analysis of a large number of materials sections. NMR
spectroscopy measurements were conducted using a Bruker Avance 400 spectrometer
(Germany) operating at 9.4 T. Proton spectra at 400 MHz were obtained using a
5-mm low proton-background probe.It is known that the
absorption of paramagnetic oxygen into aromatic polymers causes a major
shortening ofT1H  (proton longitudinal relaxation time)  [9]. Deoxygenated [9] granular samples were prepared by pumping in high vacuum
for 2 hours at 50°C in 5 mm glass tubes
followed by a sealing of the tubes. T1H recovery
curves were then measured using the saturation-recovery sequence with direct
proton observation. As a semiempirical approach to analysis, these
saturation-recovery curves were fit to a two-exponential equation according to
(1) (1)M(t)=M0s(1−e−t/T1sH)+M0l(1−e−t/T1lH), where M(t) is the
magnetization at time t, M0s and M0l are the
magnetizations of the short and long components, respectively, and T1sH and T1lH are the proton longitudinal relaxation times of
the short and long components, respectively.Qualitative
fire tests consist of burning two bar specimens shaped in accordance to ASTM D
256 norm at the same time. A Fire Testing Technology (FTT, UK)
mass loss calorimeter was used to carry out measurements on samples following the
procedure defined in ASTM E 906. The equipment is identical to that used in oxygen consumption cone
calorimetry (ASTM E-1354-90), except that a thermopile in the chimney is used
to obtain the heat release rate (HRR) rather than employing the oxygen
consumption principle. Mass loss readings are performed simultaneously by ASTM
E-1354 and serve as a benchmark of the heat release rate values obtained in
this manner. Our
procedure involved exposing specimens measuring100×100×3 mm3 in
horizontal orientation. An external heat flux of 35 kW/m2 with a cone
shaped heater was used for running the experiments. This flux corresponds to a
common heat flux in a mild fire scenario [24–27]. When
measured at 35 kW/m2, HRR is
reproducible to within +/−10%. The cone data reported in this paper are the
average of three replicated experiments.Gas permeation experiments were carried out for He,O2, and CO2 at 20°C under an upstream pressure equal to 3 bars. The permeation cell
consisted of two compartments separated by the studied membrane. The pressure
variations in the downstream compartment were measured as a function of time.
The permeability coefficient P, expressed in barrer units, was calculated from
the slope of the straight line in the steady state. The permeability data, P,
reported in this paper are the average values obtained on three samples. The
uncertainty on P value was better than 3%. The relative permeability values
were calculated for each gas from P data and the precision on this parameter
was then better than 6%.


### 2.3. Preparation of Poly(ε-Caprolactone)/clay Masterbatches

Poly(ε-caprolactone) (PCL) has been grafted on the
organoclay surface by ring-opening polymerization of ε-caprolactone
(CL) in the presence of Sn(Oct)2 according to a
“coordination-insertion” mechanism, as reported in literature [13].Before polymerization, the organomodified
montmorillonite (CL30B) (4.73 g) was dried in vacuum (10−2 mm Hg) at
70°C overnight in a glass reactor equipped with a magnetic stirrer. A toluene
solution of Sn(Oct)2  (6 mL, 3.0 10−4 mol) was then added
to the clay under nitrogen flow. A given amount of ε-caprolactone
(10 mL, 0.09 mol) was finally added such that the [monomer]0/[Sn]0 molar ratio was
300. The polymerization was carried out at 100°C for 7 days and stopped by
temperature quenching. The polyester produced was dissolved in toluene and
precipitated in heptane. The precipitate was dried in vacuum at room
temperature. A monomer conversion of 90 wt% was determined, yielding grafted PCL
chains with an Mn estimated at ca. 1500 g.mol−1, based on previously reported data [13].The clay content in the so-produced PCL-grafted CL30B nanohybrid was
checked by TGA (Q 50 from TA Instruments, 20°C/min under helium) giving an
inorganic content of 23.7 wt%. The investigated masterbatches are coded as
follows: CL30B-PCL for the grafted-PCL masterbatch.


### 2.4. Preparation of Nanocomposites

Previous studies have shown [28, 29] the possible
degradation of PCL in the presence of catalytic residues. In order to avoid any
undesirable parallel effect, Irganox MD1024 (0.05 wt%), a metal deactivator,
was blended with SAN using a Brabender internal mixer operating at 220°C for 5 minutes
with a rotation speed of 60 rpm. For the sake of simplicity, the SAN/Irganox
MD1024 blend is just noted SAN.SAN/layered silicate composites were prepared by melt blending SAN and the PCL-based
masterbatches using a Brabender internal mixer operating at 165°C for 10 minutes
with a rotation speed of 75 rpm. The collected samples were compression molded
into 3 mm-thick plates for 150 seconds at 165°C under a pressure of 150 MPa and
then rapidly cooled to room temperature.The dispersions of the
PCL-based masterbatches were carried out to produce nanocomposites containing
3 wt% of inorganics and 8.4 wt% of PCL in the presence of 0.05 wt% of Irganox
MD1024. The miscibility between the amorphous phases of SAN and PCL-grafted
within SAN/CAPA2402 and SAN/CL30B-PCL systems were evidenced by
only one intermediate Tg by DSC analysis (not shown here).Direct clay dispersions, SAN/CL30B with 3 wt% of inorganics, and binary blends,
SAN/CAPA 2402, with 8.4 wt% of PCL (in the presence of 0.05 wt% of Irganox MD1024)
have also been studied, for the sake of comparison.


## 2.1. Materials

ε-caprolactone (CL, Fluka) was dried over CaH2 and distilled under reduced pressure prior to use. Tin (II)
bis(2-ethylhexanoate), also known as tin(octoate) (Sn(Oct)2), was
purchased from Fluka (Switzerland), diluted with dried toluene, and stored
under nitrogen atmosphere.Commercial SAN, Luran 358N
(with 75 wt% of styrene) was supplied by BASF (Belgium). The SAN was systematically further
stabilized by 0.05 wt% of Irganox MD1024 supplied by CIBA (Switzerland). CAPA 2402, a PCL oligomer (Mn  = 4000 g.mol−1)
was obtained from Solvay Interox (UK). Cloisite 30B (CL30B), a montmorillonite
organomodified by 23.4 wt% of methyl bis(2-hydroxyethyl)tallowalkyl ammonium
cations was supplied by Southern Clay Products (Texas, USA).


## 2.2. Characterization

Thermogravimetric analysis (TGA) was performed at a heating rate of
20°C/min from room temperature to 800°C by using an Hi-Res TGA 2950 device from TA Instruments (Del, NY, USA). Thermodegradation was determined on approximately 15 mg samples
with platinum sample pan in a 74 cm3/min helium flow.
Thermooxidation was determined in the same way in a 69 cm3/min air
flow.The morphology of the nanocomposites has been analyzed by wide-angle
X-ray diffraction (WAXD) and atomic force microscopy (AFM). WAXD patterns were
recorded between 1.65°  and 30° (by steps of 0.04°) with a Siemens D5000
diffractometer (Germany) operating with CuKα radiation (λ=1.5406 Å). For recording AFM images, the samples were cryomicrotomed at −100°C by
an Ultracut FC4E microtome from Reichert-Jung (Austria). A truncated pyramid is
cut in the sample. Ultrathin sections of the pyramid are removed, while the ~1 × 1.5 mm2 top surface of the pyramid is imaged with AFM. The AFM
images were recorded in tapping mode (TM) with a Nanoscope IIIa microscope from
Veeco Instruments (USA). Both
height and phase images of 512×512 data points were recorded in ambient
atmosphere, at room temperature, using silicon probes with a spring constant of
24–52 N/m, a
resonance frequency in the 264–339 kHz range,
and a typical radius of curvature of 10–15 nm. The
selected AFM images are representative of the morphology of the whole sample,
as based on the analysis of a large number of materials sections. NMR
spectroscopy measurements were conducted using a Bruker Avance 400 spectrometer
(Germany) operating at 9.4 T. Proton spectra at 400 MHz were obtained using a
5-mm low proton-background probe.It is known that the
absorption of paramagnetic oxygen into aromatic polymers causes a major
shortening ofT1H  (proton longitudinal relaxation time)  [9]. Deoxygenated [9] granular samples were prepared by pumping in high vacuum
for 2 hours at 50°C in 5 mm glass tubes
followed by a sealing of the tubes. T1H recovery
curves were then measured using the saturation-recovery sequence with direct
proton observation. As a semiempirical approach to analysis, these
saturation-recovery curves were fit to a two-exponential equation according to
(1) (1)M(t)=M0s(1−e−t/T1sH)+M0l(1−e−t/T1lH), where M(t) is the
magnetization at time t, M0s and M0l are the
magnetizations of the short and long components, respectively, and T1sH and T1lH are the proton longitudinal relaxation times of
the short and long components, respectively.Qualitative
fire tests consist of burning two bar specimens shaped in accordance to ASTM D
256 norm at the same time. A Fire Testing Technology (FTT, UK)
mass loss calorimeter was used to carry out measurements on samples following the
procedure defined in ASTM E 906. The equipment is identical to that used in oxygen consumption cone
calorimetry (ASTM E-1354-90), except that a thermopile in the chimney is used
to obtain the heat release rate (HRR) rather than employing the oxygen
consumption principle. Mass loss readings are performed simultaneously by ASTM
E-1354 and serve as a benchmark of the heat release rate values obtained in
this manner. Our
procedure involved exposing specimens measuring100×100×3 mm3 in
horizontal orientation. An external heat flux of 35 kW/m2 with a cone
shaped heater was used for running the experiments. This flux corresponds to a
common heat flux in a mild fire scenario [24–27]. When
measured at 35 kW/m2, HRR is
reproducible to within +/−10%. The cone data reported in this paper are the
average of three replicated experiments.Gas permeation experiments were carried out for He,O2, and CO2 at 20°C under an upstream pressure equal to 3 bars. The permeation cell
consisted of two compartments separated by the studied membrane. The pressure
variations in the downstream compartment were measured as a function of time.
The permeability coefficient P, expressed in barrer units, was calculated from
the slope of the straight line in the steady state. The permeability data, P,
reported in this paper are the average values obtained on three samples. The
uncertainty on P value was better than 3%. The relative permeability values
were calculated for each gas from P data and the precision on this parameter
was then better than 6%.


## 2.3. Preparation of Poly(ε-Caprolactone)/clay Masterbatches

Poly(ε-caprolactone) (PCL) has been grafted on the
organoclay surface by ring-opening polymerization of ε-caprolactone
(CL) in the presence of Sn(Oct)2 according to a
“coordination-insertion” mechanism, as reported in literature [13].Before polymerization, the organomodified
montmorillonite (CL30B) (4.73 g) was dried in vacuum (10−2 mm Hg) at
70°C overnight in a glass reactor equipped with a magnetic stirrer. A toluene
solution of Sn(Oct)2  (6 mL, 3.0 10−4 mol) was then added
to the clay under nitrogen flow. A given amount of ε-caprolactone
(10 mL, 0.09 mol) was finally added such that the [monomer]0/[Sn]0 molar ratio was
300. The polymerization was carried out at 100°C for 7 days and stopped by
temperature quenching. The polyester produced was dissolved in toluene and
precipitated in heptane. The precipitate was dried in vacuum at room
temperature. A monomer conversion of 90 wt% was determined, yielding grafted PCL
chains with an Mn estimated at ca. 1500 g.mol−1, based on previously reported data [13].The clay content in the so-produced PCL-grafted CL30B nanohybrid was
checked by TGA (Q 50 from TA Instruments, 20°C/min under helium) giving an
inorganic content of 23.7 wt%. The investigated masterbatches are coded as
follows: CL30B-PCL for the grafted-PCL masterbatch.


## 2.4. Preparation of Nanocomposites

Previous studies have shown [28, 29] the possible
degradation of PCL in the presence of catalytic residues. In order to avoid any
undesirable parallel effect, Irganox MD1024 (0.05 wt%), a metal deactivator,
was blended with SAN using a Brabender internal mixer operating at 220°C for 5 minutes
with a rotation speed of 60 rpm. For the sake of simplicity, the SAN/Irganox
MD1024 blend is just noted SAN.SAN/layered silicate composites were prepared by melt blending SAN and the PCL-based
masterbatches using a Brabender internal mixer operating at 165°C for 10 minutes
with a rotation speed of 75 rpm. The collected samples were compression molded
into 3 mm-thick plates for 150 seconds at 165°C under a pressure of 150 MPa and
then rapidly cooled to room temperature.The dispersions of the
PCL-based masterbatches were carried out to produce nanocomposites containing
3 wt% of inorganics and 8.4 wt% of PCL in the presence of 0.05 wt% of Irganox
MD1024. The miscibility between the amorphous phases of SAN and PCL-grafted
within SAN/CAPA2402 and SAN/CL30B-PCL systems were evidenced by
only one intermediate Tg by DSC analysis (not shown here).Direct clay dispersions, SAN/CL30B with 3 wt% of inorganics, and binary blends,
SAN/CAPA 2402, with 8.4 wt% of PCL (in the presence of 0.05 wt% of Irganox MD1024)
have also been studied, for the sake of comparison.


## 3. Results and Discussion

To carry out
this study, several samples have been prepared by melt blending according to
the procedure reported in the experimental part. Their compositions are gathered in Table1.Table 1
Description of the studied materials.
MaterialsCompatibilizerOrganoclaySAN[a]——SAN[a]/CL30B—CL30B (3 wt% of inorganics)SAN[a]/CAPA 2402CAPA 2402 (8.4 wt% of PCL)—SAN[a]/CL30B-PCLGrafted PCL (8.4 wt% of PCL)CL30B (3 wt% of inorganics)I[a]rganox MD1024 (0.05 wt%), a metal deactivator, was blended with SAN.
The SAN/Irganox MD1024 blend is just noted SAN.


### 3.1. Materials Morphology

#### 3.1.1. Waxd and AFM Characterization of Nanocomposites

The WAXD patterns of the SAN nanocomposites
with 3 wt% of clay (SAN/CL30B and SAN/CL30B-PCL) are presented in  Figure1. Both patterns present first- and
second-order peaks related to the separation of the clay layers, indicating
that clay organization as
repetitive multilayer is preserved in the nanocomposites. The
clay interlayer distance increased from d001=1.84 nm (2θ=4.7°) in the neat organoclay (CL30B) to d001=3.2 nm (2θ=2.65°) and d001=3.6 nm (2θ=2.41°) in the SAN/CL30B and SAN/CL30B-PCL
nanocomposites, respectively. The increase
of the clay interlayer d-spacing is due to the intercalation of the polymer chains and leads to a shift of the
diffraction peak toward lower angle values, according to Bragg's law (nλ=2dsinθ, where n is an integer determined by the order given, λ is the wavelength of
X-rays, d is the spacing between the planes in the atomic lattice, and θ
is the angle between the incident ray and the scattering planes)  [1]. d002 diffraction order for SAN/CL30B and the SAN/CL30B-PCL are also detected at 2θ=5.5° and 2θ=4.7°. In addition to
intercalation, exfoliation could also occur in these nanocomposites. However,
the delamination of the platelets and their dispersion in the polymer matrix
leads to a loss of the diffraction signal. To overcome that problem, and
investigate the size and spatial distribution of the intercalated clay
aggregates, XRD measurements are complemented with AFM analyses.Figure 1
WAXD patterns of SAN/CL30B and SAN/CL30B-PCL
with 3 wt% of inorganics. The inset shows the pattern for the pristine CL30B.The first image (Figure2(a)) shows a composite obtained with the direct blend (SAN/CL30B). Large aggregates
of clay that can have dimensions up to a few microns are surrounded by a few
isolated platelets, or small stacks/aggregates, that appear as thin black lines
(the clay platelets are orthogonal to the sample surface). Despite their dimensions, the large clay aggregates are intercalated,
as deducted from WAXD (the peak corresponding to nonintercalated neat CL30B has
completely disappeared). Both the size of the large aggregates and the small
density of isolated platelets when compared to better dispersed systems suggest that the SAN
intercalation did not allow the real destructuration of the silicate aggregates;
the composite has globally the morphology of a microcomposite rather than that
of a nanocomposite. The second image (Figure 2(b))
shows on the same scale a
composite obtained with the PCL-grafted organomodified clay masterbatch
(SAN/CL30B-PCL). A much better
dispersion of clay is observed, with only isolated platelets and small
aggregates visible (again as black lines). These results are characteristics of a
semi-intercalated, semi-exfoliated structure.TMAFM phase image of SAN/CL30B and SAN/CL30B-PCL with 3 wt% of
inorganics. A clay aggregate ~10μm long is seen in the left image. Isolated
platelets and small aggregates are only visible when orthogonal to the sample
surface; they are seen as thin dark lines.
(a)(b)The most important conclusion here is that the
PCL-clay nanohybrid masterbatch technique allows obtaining a more homogeneous
and better dispersion of clay throughout the SAN matrix.


#### 3.1.2. NMR Spectroscopy Characterization of Nanocomposites

A complementary method developed at NIST [9]
has also been used to quantify the degree of nanodispersion of the layered
silicate in the SAN matrix. This method, based on solid state nuclear magnetic
resonance (NMR) of protons, uses the direct influence of the paramagnetic Fe3+ ions embedded in the aluminosilicate layers of the MMT, on polymer
protons within about 1 nm from clay platelet surface. The presence of silicate
creates “relaxation sources” which, via spin diffusion, significantly shorten
the overall T1H (proton longitudinal relaxation time). We
used T1H as an indicator of the nanodispersion of the
clay and spin diffusion modeling was used to describe this phenomenon and to
quantify the degree of nanodispersion. The main expectation is that, for a
given overall clay concentration, the better the dispersion of single MMT
layers is, the
shorter the average T1H is. T1H measurements can,
therefore, be used to probe the dispersion at the nanoscale of MMT in the
polymer. This approach, which was fully described in a previous paper
[9], thus allows determining the degree of
nanodispersion represented herewith
by the parameter f. This parameter is actually normalized to 1,
meaning that a nanocomposition displaying an f value equal or
close to 1 can be considered as fully
exfoliated. f represents the fraction of polymer/clay interface
effectively formed with respect to the maximum amount of polymer chains that
could fit around individual nanoplatelets [9]. From Table 2, we can observe that T1lH, the long components of proton
longitudinal relaxation times, are significantly shortened in the composites
with respect to the SAN matrix, as expected due to the paramagnetically induced
relaxation at the polymer-clay interface [10]. But the interesting result
concerns the dramatic decrease of T1lH, for the same clay
content, in the SAN/CL30B-PCL (3.12 seconds) system with regard to the SAN/CL30B blend (21.75 seconds). Interestingly,
the SAN/CL30B-PCL system exhibits an f value of 1 whereas the f value of the direct
blend is only 0.23. So, in agreement with previous observations by AFM and WAXD,
NMR results fully confirm that the use of the PCL/clay nanohybrid masterbatch
technique leads to a significant improvement of the organoclay nanodispersion
in the SAN matrix.Table 2
T1lH relaxation time and f parameter,
that is, the fraction of polymer/clay interface effectively formed with respect
to the maximum amount of polymer chains that could fit around individual
nanoplatelets, for SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics.
T1lH (s)fSAN41.7—SAN/CL30B21.710.23SAN/CL30B-PCL3.121These observations are of key importance to understand the properties and the
effect of clay exfoliation reported hereafter.


#### 3.1.3. Thermal Properties of Nanocomposites

As a first
step, the effects of nanoclay dispersion on both thermal and oxygen barrier
properties can be studied, qualitatively, via thermogravimetric analysis.So, the
thermal degradation behavior of SAN, SAN/CAPA 2402, SAN/CL30B, and
SAN/CL30B-PCL nanocomposites has been studied by thermogravimetric analysis
with a heating rate of 20°C/min under air or helium flow. Figure3 shows the thermogravimetric (TGA) curves and the first derivative thermogravimetric
curves (DTG) under air flow. Firstly, the maximum of the DTG curves were chosen
to compare the thermal behavior of the nanocomposites in air. Secondly, Table 3 compares the DTG maximum values in air and in helium in order to
highlight the so-called “nanoeffect” on thermal properties [7]. The
“nanoeffect” is explained by well dispersed clay layers, which hinder diffusion
of volatile decomposition products as well as oxygen penetration owing to the
increase of tortuous pathway.Table 3
Values of the maximum derivated weight loss peaks obtained from thermogravimetric analysis
(DTG) in air and in helium, at 20°C/min.
Maximum derivated weight loss peakin air (°C)Maximum derivated weight loss peak in helium (°C)SAN417435SAN/CAPA 2402423436SAN/CL30B425437SAN/CL30B-PCL436441Thermogravimetric analysis curves of SAN, SAN/CAPA 2402,
SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics in air, at 20°C/min.
(a)(b)The complete
thermal degradation behavior of SAN and SAN/CL30B has been investigated by Jang
and Wilkie [8]. Thermodegradation and thermooxidation of SAN take place in one
stage. Whatever the gas flux, the degradation pathway of SAN follows the same
degradation pathway, as described for polystyrene: chain scission followed by β-scission (depolymerization). However, in air, the chain oxidation leads
to degradation at lower temperatures. The maximum of DTG is located at 435°C in
helium versus 417°C in air (see
Table 3). In the presence of clay, only radical recombination and extensive
random scission are observed [8].The possible influence of PCL in the degradative pathway has been first
investigated for the SAN/CAPA 2402 blend. The degradation pathway of PCL has
been proposed by Stretz et al. [24]. The
thermodegradation of PCL takes place in two stages. The first process implies a
statistical rupture of the polyester chains via ester pyrolysis reaction; for
example , with CAPA 2402,
the maximum of DTG is detected close to 360°C (in air, 20°C/min). The second
step leads to the formation of ε-caprolactone (cyclic monomer) as a result of an
unzipping depolymerization process; for example, with CAPA 2402, the maximum of
DTG is detected close to 410°C (in air, 20°C/min). In the case of the
SAN(91.6%)/PCL(8.4%) blend, the DTG curve of Figure 3 shows only one degradation
step, with a maximum at 423°C in air. This result could be linked to a possible
increase of radical recombination between cleaved chains of SAN and PCL, which
leads to a delay for the weight loss.In the case of the direct blend of SAN with the organoclay (SAN/CL30B),
the maximum of DTG is recorded at 425°C in air (Figure3). This result is similar
to those obtained by Jang
and Wilkie [8] and Chu et al. [19] for equivalent composite structures. Furthermore
the comparison between the degradation temperature in air and in helium (Table
3) shows that this short delay of weight loss, which derives from the barrier
effect due to diffusion of both the volatile thermooxidation products to the
gas phase and oxygen from the gas phase to the polymer [7]  (thus the
“nanoeffect”), is not optimum because of a structure where the clay sheets are
poorly dispersed.In clear
contrast, the use of the PCL/clay nanohybrid masterbatch with the SAN/CL30B-PCL
blend leads to a longer delay of weight loss in air (Figure3). The maximum of
DTG is increased by +8°C between SAN and SAN/CL30B with respect to +19°C between SAN and
SAN/Cl30B-PCL. But the most interesting result concerns the comparison between
the degradation in air and in helium with both SAN and SAN/CL30B-PCL. Indeed,
Table 3 and Figure 4 compare the maximum of the DTG curves and the
degradation behavior of SAN and SAN/CL30B-PCL in air and in helium. Contrary to
SAN or SAN/CL30B, the degradation behavior of SAN/CL30B-PCL is almost similar
in air and in helium. This result is a characteristic of a “nanoeffect” induced
by well dispersed clay nanoplatelets. Indeed, this well dispersed clay layers
hinder diffusion of volatile decomposition products as well as oxygen
penetration thanks
to the increase of tortuous pathway, for a very low amount (3 wt%) of inorganic
nanoplatelets. This phenomenon is only obtained with nanofillers of high shape
factor [1, 7] and the same effect, with micron-sized fillers, would require much
larger amount of microparticles.Thermogravimetric analysis curves of SAN and SAN/CL30B-PCL with 3 wt%
of inorganics in air and in helium, at 20°C/min.So, the very
well dispersed clay nanocomposite obtained with a PCL/clay nanohybrid
masterbatch leads to significantly improved thermal degradation performances.These
promising results allow us to suggest that other properties could be improved
because of the large increase of the SAN/clay interface. Among others, the
flame retardancy and the gas barrier resistance properties of SAN, SAN/CL30B,
and SAN/CL30B-PCL have therefore been investigated.


#### 3.1.4. Flame Retardancy Properties of Nanocomposites

As for the flame
retardancy properties, an easy qualitative experiment consists in burning two
bar specimens of SAN and SAN/CL30B-PCL at the same time and in observing how
the samples burn. Figure5 and the support information clips illustrate
this first qualitative fire experiment. We followed the combustion of SAN (on
the left) and the SAN/CL30B-PCL nanocomposite (on the right).Qualitative flame test of SAN (on left) and SAN/CL30B-PCL (on right)
with 0.05 wt% of Irganox MD1024 and 3 wt% of inorganics. (Support information
clips:http://mail.materianova.be/pub/supportinginformationbenalietal.wmv).
(a)(b)(c)Straight away, a
different behavior is visible. The SAN specimen is burning faster than the
nanocomposite sample with an intensive dripping (i.e., continuous formation of
burning droplets). The same behavior has been observed with the direct blend
(SAN/CL30B) (not shown here). After 4 minutes, the combustion of the SAN
specimen is complete while SAN/CL30B-PCL is burning much more slowly without
any dripping. The end of the combustion is observed only after 7 minutes, and
at the end of the test, a cohesive char remains. So, this basic experiment
shows the interest of the PCL-grafting masterbatch strategy for the flame
resistance of SAN systems.The flame
retardant properties of SAN, SAN/CL30B, and SAN/CL30B-PCL have also been
investigated by mass loss cone calorimetry. In a typical experiment, the heat
release rate (HRR) developed upon materials combustion is recorded as a
function of time. Indeed, the theory of polymer nanocomposite flammability
predicts that mass transfer is altered by the presence of clay platelets [30].
Actually high aspect ratio (~100–700 nm) platelets dispersed in the matrix are known to create a tortuous
path for volatile pyrolysis products, reducing the rate at which such volatiles
can escape the condensed phase and contribute to heat release in the burning
gas phase. Furthermore the slower diffusion of the free radical products would
create a higher probability of collision and recombination (crosslinking), and
the build up of a thermally insulative char layer [21] at the surface of the
burning material. In Figure 6 it can be observed that the use of nanoclay
leads to a reduction of the peak of heat release rate (PHRR), which is a major
parameter in controlling flame propagation in fire [31]. The PHRR reduction of
the direct blend (SAN/CL30B) is similar to values reported in the literature
[10, 21] at same clay content (~−22%). The most relevant result concerns larger
PHRR reduction for the SAN/CL30-PCL sample (~−41%). Another interesting
observation concerns the residues. Samples obtained after combustion are shown
in Figure 7. No residue is observed for the SAN sample (Figure 7(a)).
Some residue trace is observed for the direct blend (SAN/CL30B)  (Figure 7(b)) with no cohesion, as also reported by Stretz and Paul [21] while significantly
larger monolithic residue, highly cohesive and homogeneous, is obtained for the
SAN/CL30B-PCL nanocomposites (Figure 7(c)). This result confirms the
importance of very well dispersed nanoclay structure to enhance the fire
retardancy properties.Figure 6
Comparison of the heat release rate (HRR) plots and peak of heat
release rate (PHRR) of SAN, SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics
at 35 kW/m2 heat flux.Photographs of the char residue recovered after cone calorimetry tests of SAN,
SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics at 35 kW/m2 heat
flux.
(a)(b)(c)


#### 3.1.5. Gas Transport Properties

From a gas transport
point of view, nanocomposites based on amorphous matrices are often considered
as a permeable continuous phase (the polymer matrix) in which impermeable
nanoplatelets are dispersed (silicate layers). An extensive explanation of
layered silicate/polymer gas transport theory has been given by Gain et al. [32]. Table 4 presents the permeability coefficients measured for SAN, SAN/CAPA
2402, SAN/CL30B, and SAN/CL30B-PCL nanocomposites for different gases (helium,
carbon dioxide, and oxygen). The permeability coefficients recorded for the SAN
matrix are similar to those given in literature [33].Table 4
Gas transport
properties of the films of SAN, SAN/CAPA 2402, SAN/CL30B, SAN/CL30B-PCL with
3 wt% of inorganics.P is the permeability coefficient.
PHe (barrer)PCO2 (barrer)PO2 (barrer)SAN14.334.431.10SAN/CAPA 240210.624.151.43SAN/CL30B9.652.990.82SAN/CL30B-PCL4.741.800.62As a first step, the
permeability of the nanocomposites is compared with that of their respective
matrix. The ratio of
SAN/CL30B nanocomposite permeability on neat SAN permeability leads to a value
of about 0.7 whatever the gas whereas the ratio of SAN/CL30B-PCL permeability
on the respective SAN/CAPA 2402 matrix permeability is much lower. Indeed a
value of 0.43 is obtained in that case for all gases. This evolution can be
directly related to the clay dispersion state in each nanocomposite. As
previously discussed, an enhanced organoclay nanodispersion leading to a higher
tortuosity effect is observed for SAN/CL30B-PCL in comparison with SAN/CL30B.Before
studying the evolution of SAN/CL30B-PCL nanocomposite gas transport properties
with respect to neat SAN, the PCL effect on SAN gas transport properties was analyzed
with the binary blend (SAN/CAPA 2402). A significant decrease of helium permeability coefficient between SAN
and SAN/CAPA 2402 is noted in Table4 whereas the carbon dioxide and oxygen
permeability variations are smaller. The PCL matrix gas transport properties
can explain these results. Indeed, the carbon dioxide and oxygen permeability
coefficients of PCL matrix are known as particularly higher than those of
unmodified SAN matrix (e.g., 13.9 barrer versus 4.43 for carbon dioxide [32] and 13 barrer versus 1.10 for oxygen [34]) while helium permeability
coefficient of PCL matrix is lower than that of SAN matrix (3.1 barrer versus
14.33 barrer)  [32]. So, the PCL effect on SAN gas transport depends on gas and
it can be taken into
account according to the additivity rule proposed for miscible systems in the
following equation: (2)ln⁡P=ϕ1⁢ln⁡P1+ϕ2⁢ln⁡P2 with P the permeability of the blend, P1 and P2 the permeability coefficients of the components of the blend, and ϕ1
and ϕ2 the volume fraction of each component in the blend.The
permeability values for the blend are 10.62 barrer versus 12.60 barrer
theoretical for helium, 1.43 barrer versus 1.35 barrer theoretical forO2, and 4.15 barrer versus 4.87 barrer theoretical for
carbon dioxide showing a relatively good agreement between experimental and
theoretical permeability values and confirming the presence of strong
interactions between SAN and PCL [33, 35].The SAN relative permeability of SAN/CAPA 2402, SAN/CL30B-PCL, and
SAN/CL30B nanocomposites is
reported in Figure8
for helium, carbon dioxide, and oxygen. In comparison with SAN/CL30B, the SAN
relative permeability of SAN/CL30B-PCL nanocomposite is lower but it depends on
the gas nature. This result can be analyzed taking into
account two main combined effects, that is, clay dispersion degree and the
presence of PCL. The higher clay exfoliation observed in SAN/CL30B-PCL in
comparison with SAN/CL30B leads to a higher decrease of the permeability. Furthermore, owing
to PCL, the SAN relative permeability properties of SAN/CL30B-PCL nanocomposite depend on the gas nature. So, the larger decrease of permeability
coefficient is measured with helium (~−67%), followed by the decrease with
carbon dioxide (~−59%) and with oxygen (~−43%).Figure 8
Relative gas permeability of SAN, SAN/CAPA 2402, SAN/CL30B, SAN/CL30B-PCL with 3 wt% of inorganics.


## 3.1. Materials Morphology

### 3.1.1. Waxd and AFM Characterization of Nanocomposites

The WAXD patterns of the SAN nanocomposites
with 3 wt% of clay (SAN/CL30B and SAN/CL30B-PCL) are presented in  Figure1. Both patterns present first- and
second-order peaks related to the separation of the clay layers, indicating
that clay organization as
repetitive multilayer is preserved in the nanocomposites. The
clay interlayer distance increased from d001=1.84 nm (2θ=4.7°) in the neat organoclay (CL30B) to d001=3.2 nm (2θ=2.65°) and d001=3.6 nm (2θ=2.41°) in the SAN/CL30B and SAN/CL30B-PCL
nanocomposites, respectively. The increase
of the clay interlayer d-spacing is due to the intercalation of the polymer chains and leads to a shift of the
diffraction peak toward lower angle values, according to Bragg's law (nλ=2dsinθ, where n is an integer determined by the order given, λ is the wavelength of
X-rays, d is the spacing between the planes in the atomic lattice, and θ
is the angle between the incident ray and the scattering planes)  [1]. d002 diffraction order for SAN/CL30B and the SAN/CL30B-PCL are also detected at 2θ=5.5° and 2θ=4.7°. In addition to
intercalation, exfoliation could also occur in these nanocomposites. However,
the delamination of the platelets and their dispersion in the polymer matrix
leads to a loss of the diffraction signal. To overcome that problem, and
investigate the size and spatial distribution of the intercalated clay
aggregates, XRD measurements are complemented with AFM analyses.Figure 1
WAXD patterns of SAN/CL30B and SAN/CL30B-PCL
with 3 wt% of inorganics. The inset shows the pattern for the pristine CL30B.The first image (Figure2(a)) shows a composite obtained with the direct blend (SAN/CL30B). Large aggregates
of clay that can have dimensions up to a few microns are surrounded by a few
isolated platelets, or small stacks/aggregates, that appear as thin black lines
(the clay platelets are orthogonal to the sample surface). Despite their dimensions, the large clay aggregates are intercalated,
as deducted from WAXD (the peak corresponding to nonintercalated neat CL30B has
completely disappeared). Both the size of the large aggregates and the small
density of isolated platelets when compared to better dispersed systems suggest that the SAN
intercalation did not allow the real destructuration of the silicate aggregates;
the composite has globally the morphology of a microcomposite rather than that
of a nanocomposite. The second image (Figure 2(b))
shows on the same scale a
composite obtained with the PCL-grafted organomodified clay masterbatch
(SAN/CL30B-PCL). A much better
dispersion of clay is observed, with only isolated platelets and small
aggregates visible (again as black lines). These results are characteristics of a
semi-intercalated, semi-exfoliated structure.TMAFM phase image of SAN/CL30B and SAN/CL30B-PCL with 3 wt% of
inorganics. A clay aggregate ~10μm long is seen in the left image. Isolated
platelets and small aggregates are only visible when orthogonal to the sample
surface; they are seen as thin dark lines.
(a)(b)The most important conclusion here is that the
PCL-clay nanohybrid masterbatch technique allows obtaining a more homogeneous
and better dispersion of clay throughout the SAN matrix.


### 3.1.2. NMR Spectroscopy Characterization of Nanocomposites

A complementary method developed at NIST [9]
has also been used to quantify the degree of nanodispersion of the layered
silicate in the SAN matrix. This method, based on solid state nuclear magnetic
resonance (NMR) of protons, uses the direct influence of the paramagnetic Fe3+ ions embedded in the aluminosilicate layers of the MMT, on polymer
protons within about 1 nm from clay platelet surface. The presence of silicate
creates “relaxation sources” which, via spin diffusion, significantly shorten
the overall T1H (proton longitudinal relaxation time). We
used T1H as an indicator of the nanodispersion of the
clay and spin diffusion modeling was used to describe this phenomenon and to
quantify the degree of nanodispersion. The main expectation is that, for a
given overall clay concentration, the better the dispersion of single MMT
layers is, the
shorter the average T1H is. T1H measurements can,
therefore, be used to probe the dispersion at the nanoscale of MMT in the
polymer. This approach, which was fully described in a previous paper
[9], thus allows determining the degree of
nanodispersion represented herewith
by the parameter f. This parameter is actually normalized to 1,
meaning that a nanocomposition displaying an f value equal or
close to 1 can be considered as fully
exfoliated. f represents the fraction of polymer/clay interface
effectively formed with respect to the maximum amount of polymer chains that
could fit around individual nanoplatelets [9]. From Table 2, we can observe that T1lH, the long components of proton
longitudinal relaxation times, are significantly shortened in the composites
with respect to the SAN matrix, as expected due to the paramagnetically induced
relaxation at the polymer-clay interface [10]. But the interesting result
concerns the dramatic decrease of T1lH, for the same clay
content, in the SAN/CL30B-PCL (3.12 seconds) system with regard to the SAN/CL30B blend (21.75 seconds). Interestingly,
the SAN/CL30B-PCL system exhibits an f value of 1 whereas the f value of the direct
blend is only 0.23. So, in agreement with previous observations by AFM and WAXD,
NMR results fully confirm that the use of the PCL/clay nanohybrid masterbatch
technique leads to a significant improvement of the organoclay nanodispersion
in the SAN matrix.Table 2
T1lH relaxation time and f parameter,
that is, the fraction of polymer/clay interface effectively formed with respect
to the maximum amount of polymer chains that could fit around individual
nanoplatelets, for SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics.
T1lH (s)fSAN41.7—SAN/CL30B21.710.23SAN/CL30B-PCL3.121These observations are of key importance to understand the properties and the
effect of clay exfoliation reported hereafter.


### 3.1.3. Thermal Properties of Nanocomposites

As a first
step, the effects of nanoclay dispersion on both thermal and oxygen barrier
properties can be studied, qualitatively, via thermogravimetric analysis.So, the
thermal degradation behavior of SAN, SAN/CAPA 2402, SAN/CL30B, and
SAN/CL30B-PCL nanocomposites has been studied by thermogravimetric analysis
with a heating rate of 20°C/min under air or helium flow. Figure3 shows the thermogravimetric (TGA) curves and the first derivative thermogravimetric
curves (DTG) under air flow. Firstly, the maximum of the DTG curves were chosen
to compare the thermal behavior of the nanocomposites in air. Secondly, Table 3 compares the DTG maximum values in air and in helium in order to
highlight the so-called “nanoeffect” on thermal properties [7]. The
“nanoeffect” is explained by well dispersed clay layers, which hinder diffusion
of volatile decomposition products as well as oxygen penetration owing to the
increase of tortuous pathway.Table 3
Values of the maximum derivated weight loss peaks obtained from thermogravimetric analysis
(DTG) in air and in helium, at 20°C/min.
Maximum derivated weight loss peakin air (°C)Maximum derivated weight loss peak in helium (°C)SAN417435SAN/CAPA 2402423436SAN/CL30B425437SAN/CL30B-PCL436441Thermogravimetric analysis curves of SAN, SAN/CAPA 2402,
SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics in air, at 20°C/min.
(a)(b)The complete
thermal degradation behavior of SAN and SAN/CL30B has been investigated by Jang
and Wilkie [8]. Thermodegradation and thermooxidation of SAN take place in one
stage. Whatever the gas flux, the degradation pathway of SAN follows the same
degradation pathway, as described for polystyrene: chain scission followed by β-scission (depolymerization). However, in air, the chain oxidation leads
to degradation at lower temperatures. The maximum of DTG is located at 435°C in
helium versus 417°C in air (see
Table 3). In the presence of clay, only radical recombination and extensive
random scission are observed [8].The possible influence of PCL in the degradative pathway has been first
investigated for the SAN/CAPA 2402 blend. The degradation pathway of PCL has
been proposed by Stretz et al. [24]. The
thermodegradation of PCL takes place in two stages. The first process implies a
statistical rupture of the polyester chains via ester pyrolysis reaction; for
example , with CAPA 2402,
the maximum of DTG is detected close to 360°C (in air, 20°C/min). The second
step leads to the formation of ε-caprolactone (cyclic monomer) as a result of an
unzipping depolymerization process; for example, with CAPA 2402, the maximum of
DTG is detected close to 410°C (in air, 20°C/min). In the case of the
SAN(91.6%)/PCL(8.4%) blend, the DTG curve of Figure 3 shows only one degradation
step, with a maximum at 423°C in air. This result could be linked to a possible
increase of radical recombination between cleaved chains of SAN and PCL, which
leads to a delay for the weight loss.In the case of the direct blend of SAN with the organoclay (SAN/CL30B),
the maximum of DTG is recorded at 425°C in air (Figure3). This result is similar
to those obtained by Jang
and Wilkie [8] and Chu et al. [19] for equivalent composite structures. Furthermore
the comparison between the degradation temperature in air and in helium (Table
3) shows that this short delay of weight loss, which derives from the barrier
effect due to diffusion of both the volatile thermooxidation products to the
gas phase and oxygen from the gas phase to the polymer [7]  (thus the
“nanoeffect”), is not optimum because of a structure where the clay sheets are
poorly dispersed.In clear
contrast, the use of the PCL/clay nanohybrid masterbatch with the SAN/CL30B-PCL
blend leads to a longer delay of weight loss in air (Figure3). The maximum of
DTG is increased by +8°C between SAN and SAN/CL30B with respect to +19°C between SAN and
SAN/Cl30B-PCL. But the most interesting result concerns the comparison between
the degradation in air and in helium with both SAN and SAN/CL30B-PCL. Indeed,
Table 3 and Figure 4 compare the maximum of the DTG curves and the
degradation behavior of SAN and SAN/CL30B-PCL in air and in helium. Contrary to
SAN or SAN/CL30B, the degradation behavior of SAN/CL30B-PCL is almost similar
in air and in helium. This result is a characteristic of a “nanoeffect” induced
by well dispersed clay nanoplatelets. Indeed, this well dispersed clay layers
hinder diffusion of volatile decomposition products as well as oxygen
penetration thanks
to the increase of tortuous pathway, for a very low amount (3 wt%) of inorganic
nanoplatelets. This phenomenon is only obtained with nanofillers of high shape
factor [1, 7] and the same effect, with micron-sized fillers, would require much
larger amount of microparticles.Thermogravimetric analysis curves of SAN and SAN/CL30B-PCL with 3 wt%
of inorganics in air and in helium, at 20°C/min.So, the very
well dispersed clay nanocomposite obtained with a PCL/clay nanohybrid
masterbatch leads to significantly improved thermal degradation performances.These
promising results allow us to suggest that other properties could be improved
because of the large increase of the SAN/clay interface. Among others, the
flame retardancy and the gas barrier resistance properties of SAN, SAN/CL30B,
and SAN/CL30B-PCL have therefore been investigated.


### 3.1.4. Flame Retardancy Properties of Nanocomposites

As for the flame
retardancy properties, an easy qualitative experiment consists in burning two
bar specimens of SAN and SAN/CL30B-PCL at the same time and in observing how
the samples burn. Figure5 and the support information clips illustrate
this first qualitative fire experiment. We followed the combustion of SAN (on
the left) and the SAN/CL30B-PCL nanocomposite (on the right).Qualitative flame test of SAN (on left) and SAN/CL30B-PCL (on right)
with 0.05 wt% of Irganox MD1024 and 3 wt% of inorganics. (Support information
clips:http://mail.materianova.be/pub/supportinginformationbenalietal.wmv).
(a)(b)(c)Straight away, a
different behavior is visible. The SAN specimen is burning faster than the
nanocomposite sample with an intensive dripping (i.e., continuous formation of
burning droplets). The same behavior has been observed with the direct blend
(SAN/CL30B) (not shown here). After 4 minutes, the combustion of the SAN
specimen is complete while SAN/CL30B-PCL is burning much more slowly without
any dripping. The end of the combustion is observed only after 7 minutes, and
at the end of the test, a cohesive char remains. So, this basic experiment
shows the interest of the PCL-grafting masterbatch strategy for the flame
resistance of SAN systems.The flame
retardant properties of SAN, SAN/CL30B, and SAN/CL30B-PCL have also been
investigated by mass loss cone calorimetry. In a typical experiment, the heat
release rate (HRR) developed upon materials combustion is recorded as a
function of time. Indeed, the theory of polymer nanocomposite flammability
predicts that mass transfer is altered by the presence of clay platelets [30].
Actually high aspect ratio (~100–700 nm) platelets dispersed in the matrix are known to create a tortuous
path for volatile pyrolysis products, reducing the rate at which such volatiles
can escape the condensed phase and contribute to heat release in the burning
gas phase. Furthermore the slower diffusion of the free radical products would
create a higher probability of collision and recombination (crosslinking), and
the build up of a thermally insulative char layer [21] at the surface of the
burning material. In Figure 6 it can be observed that the use of nanoclay
leads to a reduction of the peak of heat release rate (PHRR), which is a major
parameter in controlling flame propagation in fire [31]. The PHRR reduction of
the direct blend (SAN/CL30B) is similar to values reported in the literature
[10, 21] at same clay content (~−22%). The most relevant result concerns larger
PHRR reduction for the SAN/CL30-PCL sample (~−41%). Another interesting
observation concerns the residues. Samples obtained after combustion are shown
in Figure 7. No residue is observed for the SAN sample (Figure 7(a)).
Some residue trace is observed for the direct blend (SAN/CL30B)  (Figure 7(b)) with no cohesion, as also reported by Stretz and Paul [21] while significantly
larger monolithic residue, highly cohesive and homogeneous, is obtained for the
SAN/CL30B-PCL nanocomposites (Figure 7(c)). This result confirms the
importance of very well dispersed nanoclay structure to enhance the fire
retardancy properties.Figure 6
Comparison of the heat release rate (HRR) plots and peak of heat
release rate (PHRR) of SAN, SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics
at 35 kW/m2 heat flux.Photographs of the char residue recovered after cone calorimetry tests of SAN,
SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics at 35 kW/m2 heat
flux.
(a)(b)(c)


### 3.1.5. Gas Transport Properties

From a gas transport
point of view, nanocomposites based on amorphous matrices are often considered
as a permeable continuous phase (the polymer matrix) in which impermeable
nanoplatelets are dispersed (silicate layers). An extensive explanation of
layered silicate/polymer gas transport theory has been given by Gain et al. [32]. Table 4 presents the permeability coefficients measured for SAN, SAN/CAPA
2402, SAN/CL30B, and SAN/CL30B-PCL nanocomposites for different gases (helium,
carbon dioxide, and oxygen). The permeability coefficients recorded for the SAN
matrix are similar to those given in literature [33].Table 4
Gas transport
properties of the films of SAN, SAN/CAPA 2402, SAN/CL30B, SAN/CL30B-PCL with
3 wt% of inorganics.P is the permeability coefficient.
PHe (barrer)PCO2 (barrer)PO2 (barrer)SAN14.334.431.10SAN/CAPA 240210.624.151.43SAN/CL30B9.652.990.82SAN/CL30B-PCL4.741.800.62As a first step, the
permeability of the nanocomposites is compared with that of their respective
matrix. The ratio of
SAN/CL30B nanocomposite permeability on neat SAN permeability leads to a value
of about 0.7 whatever the gas whereas the ratio of SAN/CL30B-PCL permeability
on the respective SAN/CAPA 2402 matrix permeability is much lower. Indeed a
value of 0.43 is obtained in that case for all gases. This evolution can be
directly related to the clay dispersion state in each nanocomposite. As
previously discussed, an enhanced organoclay nanodispersion leading to a higher
tortuosity effect is observed for SAN/CL30B-PCL in comparison with SAN/CL30B.Before
studying the evolution of SAN/CL30B-PCL nanocomposite gas transport properties
with respect to neat SAN, the PCL effect on SAN gas transport properties was analyzed
with the binary blend (SAN/CAPA 2402). A significant decrease of helium permeability coefficient between SAN
and SAN/CAPA 2402 is noted in Table4 whereas the carbon dioxide and oxygen
permeability variations are smaller. The PCL matrix gas transport properties
can explain these results. Indeed, the carbon dioxide and oxygen permeability
coefficients of PCL matrix are known as particularly higher than those of
unmodified SAN matrix (e.g., 13.9 barrer versus 4.43 for carbon dioxide [32] and 13 barrer versus 1.10 for oxygen [34]) while helium permeability
coefficient of PCL matrix is lower than that of SAN matrix (3.1 barrer versus
14.33 barrer)  [32]. So, the PCL effect on SAN gas transport depends on gas and
it can be taken into
account according to the additivity rule proposed for miscible systems in the
following equation: (2)ln⁡P=ϕ1⁢ln⁡P1+ϕ2⁢ln⁡P2 with P the permeability of the blend, P1 and P2 the permeability coefficients of the components of the blend, and ϕ1
and ϕ2 the volume fraction of each component in the blend.The
permeability values for the blend are 10.62 barrer versus 12.60 barrer
theoretical for helium, 1.43 barrer versus 1.35 barrer theoretical forO2, and 4.15 barrer versus 4.87 barrer theoretical for
carbon dioxide showing a relatively good agreement between experimental and
theoretical permeability values and confirming the presence of strong
interactions between SAN and PCL [33, 35].The SAN relative permeability of SAN/CAPA 2402, SAN/CL30B-PCL, and
SAN/CL30B nanocomposites is
reported in Figure8
for helium, carbon dioxide, and oxygen. In comparison with SAN/CL30B, the SAN
relative permeability of SAN/CL30B-PCL nanocomposite is lower but it depends on
the gas nature. This result can be analyzed taking into
account two main combined effects, that is, clay dispersion degree and the
presence of PCL. The higher clay exfoliation observed in SAN/CL30B-PCL in
comparison with SAN/CL30B leads to a higher decrease of the permeability. Furthermore, owing
to PCL, the SAN relative permeability properties of SAN/CL30B-PCL nanocomposite depend on the gas nature. So, the larger decrease of permeability
coefficient is measured with helium (~−67%), followed by the decrease with
carbon dioxide (~−59%) and with oxygen (~−43%).Figure 8
Relative gas permeability of SAN, SAN/CAPA 2402, SAN/CL30B, SAN/CL30B-PCL with 3 wt% of inorganics.


## 3.1.1. Waxd and AFM Characterization of Nanocomposites

The WAXD patterns of the SAN nanocomposites
with 3 wt% of clay (SAN/CL30B and SAN/CL30B-PCL) are presented in  Figure1. Both patterns present first- and
second-order peaks related to the separation of the clay layers, indicating
that clay organization as
repetitive multilayer is preserved in the nanocomposites. The
clay interlayer distance increased from d001=1.84 nm (2θ=4.7°) in the neat organoclay (CL30B) to d001=3.2 nm (2θ=2.65°) and d001=3.6 nm (2θ=2.41°) in the SAN/CL30B and SAN/CL30B-PCL
nanocomposites, respectively. The increase
of the clay interlayer d-spacing is due to the intercalation of the polymer chains and leads to a shift of the
diffraction peak toward lower angle values, according to Bragg's law (nλ=2dsinθ, where n is an integer determined by the order given, λ is the wavelength of
X-rays, d is the spacing between the planes in the atomic lattice, and θ
is the angle between the incident ray and the scattering planes)  [1]. d002 diffraction order for SAN/CL30B and the SAN/CL30B-PCL are also detected at 2θ=5.5° and 2θ=4.7°. In addition to
intercalation, exfoliation could also occur in these nanocomposites. However,
the delamination of the platelets and their dispersion in the polymer matrix
leads to a loss of the diffraction signal. To overcome that problem, and
investigate the size and spatial distribution of the intercalated clay
aggregates, XRD measurements are complemented with AFM analyses.Figure 1
WAXD patterns of SAN/CL30B and SAN/CL30B-PCL
with 3 wt% of inorganics. The inset shows the pattern for the pristine CL30B.The first image (Figure2(a)) shows a composite obtained with the direct blend (SAN/CL30B). Large aggregates
of clay that can have dimensions up to a few microns are surrounded by a few
isolated platelets, or small stacks/aggregates, that appear as thin black lines
(the clay platelets are orthogonal to the sample surface). Despite their dimensions, the large clay aggregates are intercalated,
as deducted from WAXD (the peak corresponding to nonintercalated neat CL30B has
completely disappeared). Both the size of the large aggregates and the small
density of isolated platelets when compared to better dispersed systems suggest that the SAN
intercalation did not allow the real destructuration of the silicate aggregates;
the composite has globally the morphology of a microcomposite rather than that
of a nanocomposite. The second image (Figure 2(b))
shows on the same scale a
composite obtained with the PCL-grafted organomodified clay masterbatch
(SAN/CL30B-PCL). A much better
dispersion of clay is observed, with only isolated platelets and small
aggregates visible (again as black lines). These results are characteristics of a
semi-intercalated, semi-exfoliated structure.TMAFM phase image of SAN/CL30B and SAN/CL30B-PCL with 3 wt% of
inorganics. A clay aggregate ~10μm long is seen in the left image. Isolated
platelets and small aggregates are only visible when orthogonal to the sample
surface; they are seen as thin dark lines.
(a)(b)The most important conclusion here is that the
PCL-clay nanohybrid masterbatch technique allows obtaining a more homogeneous
and better dispersion of clay throughout the SAN matrix.


## 3.1.2. NMR Spectroscopy Characterization of Nanocomposites

A complementary method developed at NIST [9]
has also been used to quantify the degree of nanodispersion of the layered
silicate in the SAN matrix. This method, based on solid state nuclear magnetic
resonance (NMR) of protons, uses the direct influence of the paramagnetic Fe3+ ions embedded in the aluminosilicate layers of the MMT, on polymer
protons within about 1 nm from clay platelet surface. The presence of silicate
creates “relaxation sources” which, via spin diffusion, significantly shorten
the overall T1H (proton longitudinal relaxation time). We
used T1H as an indicator of the nanodispersion of the
clay and spin diffusion modeling was used to describe this phenomenon and to
quantify the degree of nanodispersion. The main expectation is that, for a
given overall clay concentration, the better the dispersion of single MMT
layers is, the
shorter the average T1H is. T1H measurements can,
therefore, be used to probe the dispersion at the nanoscale of MMT in the
polymer. This approach, which was fully described in a previous paper
[9], thus allows determining the degree of
nanodispersion represented herewith
by the parameter f. This parameter is actually normalized to 1,
meaning that a nanocomposition displaying an f value equal or
close to 1 can be considered as fully
exfoliated. f represents the fraction of polymer/clay interface
effectively formed with respect to the maximum amount of polymer chains that
could fit around individual nanoplatelets [9]. From Table 2, we can observe that T1lH, the long components of proton
longitudinal relaxation times, are significantly shortened in the composites
with respect to the SAN matrix, as expected due to the paramagnetically induced
relaxation at the polymer-clay interface [10]. But the interesting result
concerns the dramatic decrease of T1lH, for the same clay
content, in the SAN/CL30B-PCL (3.12 seconds) system with regard to the SAN/CL30B blend (21.75 seconds). Interestingly,
the SAN/CL30B-PCL system exhibits an f value of 1 whereas the f value of the direct
blend is only 0.23. So, in agreement with previous observations by AFM and WAXD,
NMR results fully confirm that the use of the PCL/clay nanohybrid masterbatch
technique leads to a significant improvement of the organoclay nanodispersion
in the SAN matrix.Table 2
T1lH relaxation time and f parameter,
that is, the fraction of polymer/clay interface effectively formed with respect
to the maximum amount of polymer chains that could fit around individual
nanoplatelets, for SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics.
T1lH (s)fSAN41.7—SAN/CL30B21.710.23SAN/CL30B-PCL3.121These observations are of key importance to understand the properties and the
effect of clay exfoliation reported hereafter.


## 3.1.3. Thermal Properties of Nanocomposites

As a first
step, the effects of nanoclay dispersion on both thermal and oxygen barrier
properties can be studied, qualitatively, via thermogravimetric analysis.So, the
thermal degradation behavior of SAN, SAN/CAPA 2402, SAN/CL30B, and
SAN/CL30B-PCL nanocomposites has been studied by thermogravimetric analysis
with a heating rate of 20°C/min under air or helium flow. Figure3 shows the thermogravimetric (TGA) curves and the first derivative thermogravimetric
curves (DTG) under air flow. Firstly, the maximum of the DTG curves were chosen
to compare the thermal behavior of the nanocomposites in air. Secondly, Table 3 compares the DTG maximum values in air and in helium in order to
highlight the so-called “nanoeffect” on thermal properties [7]. The
“nanoeffect” is explained by well dispersed clay layers, which hinder diffusion
of volatile decomposition products as well as oxygen penetration owing to the
increase of tortuous pathway.Table 3
Values of the maximum derivated weight loss peaks obtained from thermogravimetric analysis
(DTG) in air and in helium, at 20°C/min.
Maximum derivated weight loss peakin air (°C)Maximum derivated weight loss peak in helium (°C)SAN417435SAN/CAPA 2402423436SAN/CL30B425437SAN/CL30B-PCL436441Thermogravimetric analysis curves of SAN, SAN/CAPA 2402,
SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics in air, at 20°C/min.
(a)(b)The complete
thermal degradation behavior of SAN and SAN/CL30B has been investigated by Jang
and Wilkie [8]. Thermodegradation and thermooxidation of SAN take place in one
stage. Whatever the gas flux, the degradation pathway of SAN follows the same
degradation pathway, as described for polystyrene: chain scission followed by β-scission (depolymerization). However, in air, the chain oxidation leads
to degradation at lower temperatures. The maximum of DTG is located at 435°C in
helium versus 417°C in air (see
Table 3). In the presence of clay, only radical recombination and extensive
random scission are observed [8].The possible influence of PCL in the degradative pathway has been first
investigated for the SAN/CAPA 2402 blend. The degradation pathway of PCL has
been proposed by Stretz et al. [24]. The
thermodegradation of PCL takes place in two stages. The first process implies a
statistical rupture of the polyester chains via ester pyrolysis reaction; for
example , with CAPA 2402,
the maximum of DTG is detected close to 360°C (in air, 20°C/min). The second
step leads to the formation of ε-caprolactone (cyclic monomer) as a result of an
unzipping depolymerization process; for example, with CAPA 2402, the maximum of
DTG is detected close to 410°C (in air, 20°C/min). In the case of the
SAN(91.6%)/PCL(8.4%) blend, the DTG curve of Figure 3 shows only one degradation
step, with a maximum at 423°C in air. This result could be linked to a possible
increase of radical recombination between cleaved chains of SAN and PCL, which
leads to a delay for the weight loss.In the case of the direct blend of SAN with the organoclay (SAN/CL30B),
the maximum of DTG is recorded at 425°C in air (Figure3). This result is similar
to those obtained by Jang
and Wilkie [8] and Chu et al. [19] for equivalent composite structures. Furthermore
the comparison between the degradation temperature in air and in helium (Table
3) shows that this short delay of weight loss, which derives from the barrier
effect due to diffusion of both the volatile thermooxidation products to the
gas phase and oxygen from the gas phase to the polymer [7]  (thus the
“nanoeffect”), is not optimum because of a structure where the clay sheets are
poorly dispersed.In clear
contrast, the use of the PCL/clay nanohybrid masterbatch with the SAN/CL30B-PCL
blend leads to a longer delay of weight loss in air (Figure3). The maximum of
DTG is increased by +8°C between SAN and SAN/CL30B with respect to +19°C between SAN and
SAN/Cl30B-PCL. But the most interesting result concerns the comparison between
the degradation in air and in helium with both SAN and SAN/CL30B-PCL. Indeed,
Table 3 and Figure 4 compare the maximum of the DTG curves and the
degradation behavior of SAN and SAN/CL30B-PCL in air and in helium. Contrary to
SAN or SAN/CL30B, the degradation behavior of SAN/CL30B-PCL is almost similar
in air and in helium. This result is a characteristic of a “nanoeffect” induced
by well dispersed clay nanoplatelets. Indeed, this well dispersed clay layers
hinder diffusion of volatile decomposition products as well as oxygen
penetration thanks
to the increase of tortuous pathway, for a very low amount (3 wt%) of inorganic
nanoplatelets. This phenomenon is only obtained with nanofillers of high shape
factor [1, 7] and the same effect, with micron-sized fillers, would require much
larger amount of microparticles.Thermogravimetric analysis curves of SAN and SAN/CL30B-PCL with 3 wt%
of inorganics in air and in helium, at 20°C/min.So, the very
well dispersed clay nanocomposite obtained with a PCL/clay nanohybrid
masterbatch leads to significantly improved thermal degradation performances.These
promising results allow us to suggest that other properties could be improved
because of the large increase of the SAN/clay interface. Among others, the
flame retardancy and the gas barrier resistance properties of SAN, SAN/CL30B,
and SAN/CL30B-PCL have therefore been investigated.


## 3.1.4. Flame Retardancy Properties of Nanocomposites

As for the flame
retardancy properties, an easy qualitative experiment consists in burning two
bar specimens of SAN and SAN/CL30B-PCL at the same time and in observing how
the samples burn. Figure5 and the support information clips illustrate
this first qualitative fire experiment. We followed the combustion of SAN (on
the left) and the SAN/CL30B-PCL nanocomposite (on the right).Qualitative flame test of SAN (on left) and SAN/CL30B-PCL (on right)
with 0.05 wt% of Irganox MD1024 and 3 wt% of inorganics. (Support information
clips:http://mail.materianova.be/pub/supportinginformationbenalietal.wmv).
(a)(b)(c)Straight away, a
different behavior is visible. The SAN specimen is burning faster than the
nanocomposite sample with an intensive dripping (i.e., continuous formation of
burning droplets). The same behavior has been observed with the direct blend
(SAN/CL30B) (not shown here). After 4 minutes, the combustion of the SAN
specimen is complete while SAN/CL30B-PCL is burning much more slowly without
any dripping. The end of the combustion is observed only after 7 minutes, and
at the end of the test, a cohesive char remains. So, this basic experiment
shows the interest of the PCL-grafting masterbatch strategy for the flame
resistance of SAN systems.The flame
retardant properties of SAN, SAN/CL30B, and SAN/CL30B-PCL have also been
investigated by mass loss cone calorimetry. In a typical experiment, the heat
release rate (HRR) developed upon materials combustion is recorded as a
function of time. Indeed, the theory of polymer nanocomposite flammability
predicts that mass transfer is altered by the presence of clay platelets [30].
Actually high aspect ratio (~100–700 nm) platelets dispersed in the matrix are known to create a tortuous
path for volatile pyrolysis products, reducing the rate at which such volatiles
can escape the condensed phase and contribute to heat release in the burning
gas phase. Furthermore the slower diffusion of the free radical products would
create a higher probability of collision and recombination (crosslinking), and
the build up of a thermally insulative char layer [21] at the surface of the
burning material. In Figure 6 it can be observed that the use of nanoclay
leads to a reduction of the peak of heat release rate (PHRR), which is a major
parameter in controlling flame propagation in fire [31]. The PHRR reduction of
the direct blend (SAN/CL30B) is similar to values reported in the literature
[10, 21] at same clay content (~−22%). The most relevant result concerns larger
PHRR reduction for the SAN/CL30-PCL sample (~−41%). Another interesting
observation concerns the residues. Samples obtained after combustion are shown
in Figure 7. No residue is observed for the SAN sample (Figure 7(a)).
Some residue trace is observed for the direct blend (SAN/CL30B)  (Figure 7(b)) with no cohesion, as also reported by Stretz and Paul [21] while significantly
larger monolithic residue, highly cohesive and homogeneous, is obtained for the
SAN/CL30B-PCL nanocomposites (Figure 7(c)). This result confirms the
importance of very well dispersed nanoclay structure to enhance the fire
retardancy properties.Figure 6
Comparison of the heat release rate (HRR) plots and peak of heat
release rate (PHRR) of SAN, SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics
at 35 kW/m2 heat flux.Photographs of the char residue recovered after cone calorimetry tests of SAN,
SAN/CL30B and SAN/CL30B-PCL with 3 wt% of inorganics at 35 kW/m2 heat
flux.
(a)(b)(c)


## 3.1.5. Gas Transport Properties

From a gas transport
point of view, nanocomposites based on amorphous matrices are often considered
as a permeable continuous phase (the polymer matrix) in which impermeable
nanoplatelets are dispersed (silicate layers). An extensive explanation of
layered silicate/polymer gas transport theory has been given by Gain et al. [32]. Table 4 presents the permeability coefficients measured for SAN, SAN/CAPA
2402, SAN/CL30B, and SAN/CL30B-PCL nanocomposites for different gases (helium,
carbon dioxide, and oxygen). The permeability coefficients recorded for the SAN
matrix are similar to those given in literature [33].Table 4
Gas transport
properties of the films of SAN, SAN/CAPA 2402, SAN/CL30B, SAN/CL30B-PCL with
3 wt% of inorganics.P is the permeability coefficient.
PHe (barrer)PCO2 (barrer)PO2 (barrer)SAN14.334.431.10SAN/CAPA 240210.624.151.43SAN/CL30B9.652.990.82SAN/CL30B-PCL4.741.800.62As a first step, the
permeability of the nanocomposites is compared with that of their respective
matrix. The ratio of
SAN/CL30B nanocomposite permeability on neat SAN permeability leads to a value
of about 0.7 whatever the gas whereas the ratio of SAN/CL30B-PCL permeability
on the respective SAN/CAPA 2402 matrix permeability is much lower. Indeed a
value of 0.43 is obtained in that case for all gases. This evolution can be
directly related to the clay dispersion state in each nanocomposite. As
previously discussed, an enhanced organoclay nanodispersion leading to a higher
tortuosity effect is observed for SAN/CL30B-PCL in comparison with SAN/CL30B.Before
studying the evolution of SAN/CL30B-PCL nanocomposite gas transport properties
with respect to neat SAN, the PCL effect on SAN gas transport properties was analyzed
with the binary blend (SAN/CAPA 2402). A significant decrease of helium permeability coefficient between SAN
and SAN/CAPA 2402 is noted in Table4 whereas the carbon dioxide and oxygen
permeability variations are smaller. The PCL matrix gas transport properties
can explain these results. Indeed, the carbon dioxide and oxygen permeability
coefficients of PCL matrix are known as particularly higher than those of
unmodified SAN matrix (e.g., 13.9 barrer versus 4.43 for carbon dioxide [32] and 13 barrer versus 1.10 for oxygen [34]) while helium permeability
coefficient of PCL matrix is lower than that of SAN matrix (3.1 barrer versus
14.33 barrer)  [32]. So, the PCL effect on SAN gas transport depends on gas and
it can be taken into
account according to the additivity rule proposed for miscible systems in the
following equation: (2)ln⁡P=ϕ1⁢ln⁡P1+ϕ2⁢ln⁡P2 with P the permeability of the blend, P1 and P2 the permeability coefficients of the components of the blend, and ϕ1
and ϕ2 the volume fraction of each component in the blend.The
permeability values for the blend are 10.62 barrer versus 12.60 barrer
theoretical for helium, 1.43 barrer versus 1.35 barrer theoretical forO2, and 4.15 barrer versus 4.87 barrer theoretical for
carbon dioxide showing a relatively good agreement between experimental and
theoretical permeability values and confirming the presence of strong
interactions between SAN and PCL [33, 35].The SAN relative permeability of SAN/CAPA 2402, SAN/CL30B-PCL, and
SAN/CL30B nanocomposites is
reported in Figure8
for helium, carbon dioxide, and oxygen. In comparison with SAN/CL30B, the SAN
relative permeability of SAN/CL30B-PCL nanocomposite is lower but it depends on
the gas nature. This result can be analyzed taking into
account two main combined effects, that is, clay dispersion degree and the
presence of PCL. The higher clay exfoliation observed in SAN/CL30B-PCL in
comparison with SAN/CL30B leads to a higher decrease of the permeability. Furthermore, owing
to PCL, the SAN relative permeability properties of SAN/CL30B-PCL nanocomposite depend on the gas nature. So, the larger decrease of permeability
coefficient is measured with helium (~−67%), followed by the decrease with
carbon dioxide (~−59%) and with oxygen (~−43%).Figure 8
Relative gas permeability of SAN, SAN/CAPA 2402, SAN/CL30B, SAN/CL30B-PCL with 3 wt% of inorganics.


## 4. Conclusion

Semi-intercalated, semi-exfoliated SAN/layered silicate nanocomposites
have been prepared using PCL-grafted organoclay nanohybrids as masterbatch to
substantially increase the degree of exfoliation. The PCL-grafted organoclay nanohybrids are
added as masterbatches in SAN by melt blending. This two-step preparation of
nanocomposites leads to very well dispersed clay nanocomposites with 3 wt% of
inorganics. Morphological (WAXD and AFM analyses) and solid state NMR
spectroscopy measurements confirm a more delaminated structure in SAN
nanocomposites based on PCL-clay nanohybrid masterbatch
(SAN/CL30B-PCL) while only an intercalated structure is found with the direct
blend (SAN/CL30B). So,
a strong improvement of both fire retardancy and barrier gases resistance
properties has been found with the SAN/CL30B-PCL nanocomposite, which reflects
the large superiority of the PCL-clay nanohybrid masterbatches strategy over
the direct blend for the SAN matrix. A decrease up to 40% of PHRR is noted with
SAN/CL30B-PCL versus less than 20% with SAN/CL30B and the permeability
coefficient is widely decreased (up to 67% with SAN/CL30B-PCL versus only 30%
with SAN/CL30B for helium).As indicated
in the introduction, this study is
part of a larger study, which aims at developing SAN foams. So, in this
specific application context it would be interesting to study more extensively
the interest of PCL/clay nanohybrid masterbatches on the mechanical, flame
retardancy and gas barrier properties of SAN foams.Furthermore, the SAN
matrix is considered as a model system useful [24] to understand
acrylonitrile-butadiene-styrene (ABS). So, it would be interesting to extend
the use of PCL/clay nanohybrid masterbatches to ABS materials. Indeed, ABS/clay
systems may have several applications, including fire-retarded formulations for
recyclable computer housing [24].



---

*Source: 394235-2009-04-16.xml*