Bio-based semi-aromatic polyamide/functional clay nanocomposites: Preparation and properties

Article abstract of DOI:10.1039/c4ra02949f

In this paper we first describe the design and synthesis of two novel cationic functional modifiers, i.e. a functionalized β-cyclodextrin (β-CD) derivative and tris(3-aminophenyl)phenyl phosphine oxide (TAP). Cloisite Na⁺ (clay-Na) and the modifiers were used for the preparation of the organoclay containing phosphine oxide (clay-PO) and of the organoclay containing β-cyclodextrin (clay-CD) via ion-exchange reaction. Biobased semi-aromatic polyamide (BPA)/functional clay (clay-PO and clay-CD) nanocomposites subsequently were prepared via solution blending. Effects of the two different types of organoclays on the flammable, thermal and mechanical properties of these biobased semi-aromatic polyamide nanocomposites were then studied. The properties of the nanocomposites were found to be strongly related to the nature of the modifiers. The clay-CD based nanocomposites (BPACD) showed more enhancements in thermal stability. The modifier containing the phosphine oxide moiety and triamine groups had stronger interactions with the polymer matrix, and exhibited superior mechanical properties, good flame retardancy and high thermal stability. Thus, we provide a new approach for comprehensive improvement of the properties of these bio-based semi-aromatic polyamide nanocomposite materials.

Full text of DOI:10.1039/c4ra02949f

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PAPER
Bio-based semi-aromatic polyamide/functional
clay nanocomposites: preparation and properties†
Cite this: RSC Adv., 2014, 4, 23420
Meisam Shabanian,bc Nianjun Kang,a Jianwen Liu,b Udo Wagenknecht,b
a
Gert Heinrichbd and De-Yi Wang
*
In this paper we first describe the design and synthesis of two novel cationic functional modifiers, i.e. a
functionalized b-cyclodextrin (b-CD) derivative and tris(3-aminophenyl)phenyl phosphine oxide (TAP).
Cloisite Na+ (clay-Na) and the modifiers were used for the preparation of the organoclay containing
phosphine oxide (clay-P]O) and of the organoclay containing b-cyclodextrin (clay-CD) via ion-
exchange reaction. Biobased semi-aromatic polyamide (BPA)/functional clay (clay-P]O and clay-CD)
nanocomposites subsequently were prepared via solution blending. Effects of the two different types of
organoclays on the flammable, thermal and mechanical properties of these biobased semi-aromatic
polyamide nanocomposites were then studied. The properties of the nanocomposites were found to be
strongly related to the nature of the modifiers. The clay-CD based nanocomposites (BPACD) showed
more enhancements in thermal stability. The modifier containing the phosphine oxide moiety and
triamine groups had stronger interactions with the polymer matrix, and exhibited superior mechanical
properties, good flame retardancy and high thermal stability. Thus, we provide a new approach for
comprehensive improvement of the properties of these bio-based semi-aromatic polyamide
nanocomposite materials.
Received 2nd April 2014
Accepted 1st May 2014
DOI: 10.1039/c4ra02949f
www.rsc.org/advances
cyclodextrin subtype is b-cyclodextrin, which consists of seven
glucose units.
1. Introduction
Bio-composites provide an option for the use of new, high
performance, “green” composite materials instead of conven-
tional petroleum-based plastic materials. In the preparation of
bio-composites and/or polymer nanocomposites, organically
modied montmorillonites (O-MMT) are most widely used.7–10
Clays are generally organomodied or functionalized in order to
form strong interactions between the polymer matrix and
nanoclays. Organomodication of clay-Na+ is very important for
the nanocomposites, since interactions between the polymer
matrix and the nanoclays signicantly inuence the compre-
hensive properties of polymer nanocomposites. Fornes et al.11
investigated the properties of polyamide-6 (PA6)/montmoril-
lonite by using different organic modiers, and found that the
surfactant structure affected the morphology and properties of
nylon 6 nanocomposites. It is found that most conventional
modiers of clay are ammable, and that the ammability of
these materials ultimately limits the ame retardant properties
of polymer nanocomposites. Therefore, modiers with low
ammability and strong interactive properties become very
important in the development of high performance clay based
polymer nanocomposites. As an example of this, Wang et al.
have developed a b-cyclodextrin-based layered double hydroxide
(LDH) material with low ammability.12
In anticipation of the growing need for sustainable materials for
the next century, utilization of natural renewable resources
becomes an important consideration.1 Various materials from
nontoxic plant/crop-based resources and biobased renewable
products are strategic options that may be considered as alter-
natives to petroleum-based products. The most widely used
renewable resource materials include polysaccharides, vege-
table oils, wood and proteins. Various materials have been
prepared from these naturally occurring renewable resources.2–5
Cyclodextrins belong to the family of cyclic homologous oligo-
saccharides that are obtained from the enzymatic degradation
of starch. Cyclodextrins are composed of six or more a-D-glu-
copyranose units that are joined at the 1,4 positions by a-
glucosidic linkages.6 The most commonly used natural
aMadrid Institute for Advanced Studies of Materials (IMDEA Materials), C/Eric Kandel,
2, 28906 Getafe, Madrid, Spain. E-mail: deyi.wang@imdea.org
b
¨
Leibniz-Institut fur Polymerforschung Dresden e.V., Hohe Strasse 6, D-01069 Dresden,
Germany
cFaculty of Chemistry and Petrochemical Engineering, Standard Research Institute
(SRI), P.O. Box 31745-139, Karaj, Iran
d
¨
¨
Technische Universitat Dresden, Institut fur Werkstoffwissenscha, D-01069 Dresden,
Germany
Aromatic polyamides (a group of versatile high-performance
polymers) display a wide range of applications and properties,
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra02949f
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and are useful for advanced technologies.13,14 However, their low
solubility and high glass transition temperature oen provide
problems with their application. In order to address these
problems, the use of semi-aromatic polyamides (synthesized via
a combination of aliphatic and aromatic monomers) is regar-
ded as a promising alternative. Semi-aromatic polyamides are
generally exploited to ll the “performance gap” between high-
performance polymers and nylons such as PA6.15 Such poly-
amides offer a wide range of properties including transparency,
outstanding strength-to-weight ratios, high thermal resistance,
and good barrier and solvent resistant properties, respec-
tively.16–21 In our latest work, a novel biobased semi-aromatic
polyamide (BPA) derived from nonanedioic acid and aromatic
diamine containing a pyridine group has been synthesized and
characterized.22 However, it has been found that while the use of
conventional nanoclay (Cloisite 30B) can slightly improve the
ame retardancy of BPA materials, it also severely decreases
their mechanical properties.
Scheme 1 Preparation of BPACD and BPAPO.
In order to obtain high performance biobased semi-aromatic
polyamide (BPA) nanocomposites, two new nanoclays were
synthesized and characterized by using two functional modi-
ers containing modied phosphine oxide and modied b-
cyclodextrin, respectively. BPA/organoclay nanocomposites
then were prepared via solution blending. Effects of the two new
organoclays on the morphology, thermal, ammability and
mechanical properties of the BPA nanocomposites were inves-
tigated, and our ndings are reported below.
150 mL of glacial acetic acid were reuxed for 18 hours. Upon
cooling, the precipitated yellow solid was collected by ltration
and washed with ethanol. The yield of the crude product was
68%, with a melting point of 285 ꢀC (see Scheme 1).
2.2.3 Synthesis of 4-(4-hydroxyphenyl)-2,6-bis(4-amino-
phenyl)pyridine. In a 250 mL round-bottomed ask equipped
with a reux condenser and a dropping funnel, a suspension of
the synthesized dinitro compound (5 g, 12 mmol); palladium on
carbon 10% (0.1 g); ethanol (30 mL); and dimethylformamide
(DMF, 5 mL) was prepared. The mixture was warmed, and while
being stirred magnetically, hydrazine monohydrate 80% (10 mL)
in ethanol (15 mL) was added dropwise over a 1 hour period
through a dropping funnel, while keeping the temperature at
about 70 ꢀC. Aer 4 hours, the mixture was ltered while hot to
remove Pd/C, and the solvent then evaporated under vacuum to
afford the yellow solid product (yield, 94%; melting point, 230 ꢀC;
1H NMR (500 MHz, DMSO) d, ppm: 9.7 (s, 1H), 8.0 (d, 4H), 7.8 (d,
2H), 7.7 (s, 2H), 6.9 (d, 2H), 6.7 (d, 4H), 5.4 (d, 4H); see Scheme 1).
2.2.4 Synthesis of biobased aliphatic–aromatic polyamide.
4-(4-hydroxyphenyl)-2,6-bis(4-aminophenyl)pyridine (5 g, 14
mmol); nonanedioic acid (2.7 g, 14 mmol); calcium chloride
(0.5 g, 4.5 mmol); triphenyl phosphite (8.7 mL, 28 mmol);
pyridine (1 mL); and N-methyl-2-pyrrolidone (8 mL) were added
to a 50 mL round-bottomed ask tted with a stirring bar. The
reaction mixture was heated under reux in an oil bath atꢀ60 ꢀC
2. Experimental
2.1 Materials
b-cyclodextrin, allyl glycidyl ether (AGE) and (3-chloro-2-
hydroxypropyl)trimethylammonium chloride (CMA) were
obtained from ABCR GmbH & Co. KG in Germany, and used
without further purication. Triphenylphosphine oxide, palla-
dium charcoal, N-methyl-2-pyrrolidone (NMP), N,N-dimethyla-
cetamide (DMAc), hydrazine hydrate, pyridine, nitric acid,
sulfuric acid, methanol, triphenyl phosphite (TPP), oleic acid, 4-
nitroacetophenone,
4-hydroxybenzaldehyde,
ammonium
acetate, potassium permanganate (KMnO4) and glacial acetic
acid obtained from Aldrich were used without further puri-
cation. Sodium montmorillonite (NaMMT; unmodied having
CEC ¼ 92.6 meq. per 100 g clay) from Southern Clay Products,
Inc. was used.
ꢀ
for 1 hour, then at 90 C for 3 hours, and nally at 120 C for
Commercially available calcium chloride (CaCl2, Aldrich)
ꢀ
8 hours. The reaction mixture was then poured into 100 mL of
methanol, and the precipitated product collected by ltration
and washed thoroughly with hot methanol. Finally, the product
was dried at 60 ꢀC for 12 hours in a vacuum oven until a
constant weight was attained (yield, 95%).
was dried under vacuum at 150 C for 6 hours.
2.2 Synthesis of semi-aromatic biobased polyamide (BPA)22
2.2.1 Synthesis of nonanedioic acid from oleic acid.
KMnO4 was used to oxidize the double bond of the oleic acid,
forming nonanedioic acid, following procedures in the litera-
ture23 (yield: 67%).
2.2.2 Synthesis of 4-(4-hydroxyphenyl)-2,6-bis(4-nitrophenyl)
pyridine. In a 500 mL round-bottomed ask, a mixture of 5.0 g
2.3 Synthesis of b-cyclodextrin based modier (CD-DB-N+)
and tris(3-aminophenyl)phenyl phosphine oxide based
modier
(41 mmol) of 4-hydroxybenzaldehyde; 13.5 g (82 mmol) of In a 50 mL round-bottomed ask, 4.54 g b-CD (4 mmol) was
4-nitroacetophenone; 76.5 g (1.0 mol) of ammonium acetate; and added with stirring to an aqueous solution composed of 15 mL
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water and 3.0 g NaOH maintained at 70 ꢀC. Subsequently, 1.83 g
Wide angle X-ray scattering (WAXS) was performed using a
(16 mmol) AGE was slowly added, and the mixture was stirred 2-circle diffractometer XRD 3003 q/q (GE Inspection Technolo-
for 6 hours. Following this, 5.45 g (40 mmol) CMA solution was gies/Seifert-FPM, Freiberg, Germany) with Cu-Ka radiation
slowly added with vigorous stirring. Aer the reaction was (l ¼ 0.154 nm) generated at 30 mA and 40 kV in the range of
complete, the solution was cooled to room temperature and 2q ¼ 2–12ꢀ using 0.05ꢀ as the step length.
diluted with 30 mL water. The resulting solution was neutral-
Thermal stability of the samples was investigated by ther-
ized with 1 M hydrochloric acid and dialyzed against 3 ꢁ mogravimetric analysis (TGA; TA instruments Q 5000) in the
700 mL water to remove salts (3-allyloxy-1,2-propanediol and range between room temperature and 800 ꢀC at a heating rate of
hydroxyalkyl ammonium, respectively) formed as side products. 10 ꢀC minꢂ1 in a nitrogen atmosphere. The glass transition
The dialysate was then poured out into 100 mL of ethanol. The temperatures of samples were measured by differential scan-
precipitate was ltered and dried under vacuum at 80 ꢀC for ning calorimetry (DSC, TA instrument Q1000) in the range
12 hours.
between 80 ꢀC and 230 ꢀC at a heating rate of 10 ꢀC minꢂ1 in a
Triamine containing phosphorus was synthesized in the nitrogen atmosphere.
laboratory according to the procedure reported elsewhere.24
Microscale combustion calorimetry (MCC-1, FTT) is a
convenient and relatively new technique developed in recent
years for investigating the ammability of polymers.25,26 Using
this technique, samples of approximately 5 mg mass were
heated to 700 ꢀC at a heating rate of 1 ꢀC sꢂ1 in a stream of
nitrogen owing at 80 cm3 minꢂ1. The volatile, anaerobic
thermal degradation products were then mixed with a 20 cm3
minꢂ1 gas stream containing 20% oxygen and 80% nitrogen,
2.4 Functional modication of nanoclays
Clay-CD was prepared by a cation exchange method. Clay-Na
(5 g) was dispersed in 700 mL distilled water at room temper-
ature. Another solution containing 2 g of CD-DB-N+ in 40 mL
distilled water was prepared using magnetic stirring, and with
the addition of 1.0 M HCl aqueous solution to adjust the pH
value to 3–4. This solution was added to the clay suspension at a
rate of approximately 15 mL minꢂ1 with vigorous stirring. The
mixture was stirred overnight at room temperature. Aerward,
the organoclay was ltering using a Buchner funnel. The
resulting organoclay (clay-CD) was washed with distilled water
to remove any excess ammonium ions. The same procedure was
used to prepare the organoclay based on the cationic form of
TAP (clay-P]O).
ꢀ
respectively, prior to entering a 900 C combustion furnace.
Tensile testing of the lms was performed with FAVIGRAPH
semiautomatic
instrumentation
(Textechno
Company,
Germany), equipped with a 100 N load cell. Specimens of 20 mm
gauge length, 40–60 mm thickness, and 3 mm width were tested
at a speed of 10 mm minꢂ1. Relative humidity was kept at 50%
and the temperature at 23 ꢀC. Modulus strain between
0.1ꢂ0.2% was determined by stress–strain curve analysis.
3. Results and discussion
2.5 Preparation of BPA/organoclay nanocomposites
3.1 Synthesis and characterization of functional modiers
The nanocomposites were synthesized by taking the BPA solu-
tion in a ask, followed by the addition of an appropriate
amount of the organoclay at particular concentrations (see
Scheme 1). For example, to prepare a nanocomposite contain-
ing 2 wt% of clay-CD, 0.98 g of the BPA was dissolved in DMAc in
a 50 mL ask, followed by the addition of 0.02 g of clay-CD. The
The modied b-cyclodextrin was obtained by the reaction of
hydroxyl groups in b-cyclodextrin with the electrophilic groups
of AGE and CMA via a two-step reaction (Scheme 2). Structure
conformation was determined by means of 1H NMR. As shown
in Fig. 1, the singlet peak at 5.87 ppm was assigned to the
ꢀ
reaction mixture was agitated at high speed at 25 C overnight
to disperse clay platelets uniformly in the BPA matrix. The
amount of clay-CD was 2 and 4 wt% in the nanocomposites
(BPACD 2 and BPACD 4), respectively. By casting the suspension
onto a glass plate followed by solvent evaporation in a vacuum
oven, the nal BPA nanocomposite lms were prepared. The
nanocomposites with the BPA and clay-P]O (BPAPO 2 and
BPAPO 4) were prepared using the same procedure.
2.6 Characterization
1H-NMR measurements were performed with a Bruker Avance
III 500 spectrometer (Rheinstetten, Germany) operating at 500
MHz. DMSO-d6 was used as the solvent and the solvent signal
was used for internal calibration (DMSO-d6: d(1H) ¼ 2.5 ppm).
Morphological analysis was carried out using a LEO 912
transmission electron microscope. The conditions used during
analysis were room temperature, 120 kV acceleration voltage,
and bright eld illumination.
Scheme 2 The structure and synthesis route of the two modifiers.
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proton on the carbon carbon double bonds (–CH]CH2) on the
structure of AGE segments (corresponding to C1 in Fig. 1), while
the peak at 4.21 ppm was assigned to protons on the CMA
segment (corresponding to C3 in Fig. 1). All these NMR char-
acteristic peaks matched the expected CD-DB-N+ structure.
During the reaction, the protons of C2 on b-CD (Fig. 2) were not
affected. For this reason, the ratio of the integrated peak for C2–
H over that of C1–H at 5.87 ppm and C4–H at 3.25 ppm was used
to estimate the number of carbon carbon double bonds and
cationic segments graed. By calculation, the ratio of C4–H/C2–
H was 7.28, indicating that 5.66 cationic segments were
attached per b-CD molecule. The ratio of C1–H/C2–H was 0.75,
indicating that 5.25 carbon carbon double bonds were attached
per b-CD molecule.
3.2 Characterization of the nanocomposites
3.2.1 X-ray diffraction. XRD patterns of each organoclay
and its corresponding nanocomposite are shown in Fig. 3. XRD
provided information on the change of interlayer spacing of the
clay upon formation of a nanocomposite. X-ray results of
modied nanoclays revealed that intercalation behaviors were
successfully accomplished by using the new modiers of
CD-DB-N+ and TAP-N+. More specically, the interlayer
d-spacing of the nanoclays increased aer the ion-exchange
process by the modiers in comparison to that of the clay-Na+.
For example, the d-spacing of unmodied clay (clay-Na+) is
1.17 nm, calculated from the reection at 2q ¼ 7.6ꢀ using
Bragg's equation. Aer the ion-exchange reaction with the
ammonium salt of TAP, reection of the clay shied to a new
position at 2q ¼ 5.4ꢀ (d ¼ 1.63 nm) in clay-P]O. An increase of
the interlayer distance led to a shi of the reection and an
increase in the basal spacing, providing evidence that interca-
lation had occurred. Similarly, it was noted that the d-spacing of
clay-CD was 1.42 nm which was calculated from the reection at
2q ¼ 6.2ꢀ. These ndings indicate that the functional nanoclays,
clay-P]O and clay-CD, were prepared successfully.
TAP was synthesized from triphenyl phosphine oxide, and
rst converted to tris(3-nitrophenyl)phenyl phosphine oxide by
using concentrated nitric acid in the presence of sulfuric acid.
Tris(3-nitrophenyl)phenyl phosphine oxide was then reduced to
TAP with Pd/C and NH2NH2 (Scheme 1).
1H NMR (500 MHz, DMSO) d, ppm of TAP: 7.10–7.14 (m, 3H),
6.84–6.87 (d, 3H), 6.71–6.73 (d, 3H), 6.62–6.65 (q, 4H), 5.33
(s, 6H).
Fig. 3 also displays XRD patterns of BPA and corresponding
nanocomposites. Composite lms containing 2 and 4 wt%,
respectively, of the two different organoclays showed no peak in
the region 2q ¼ 2–12. No peaks in XRD patterns were observed
for the BPA nanocomposites. This might mean that the orga-
noclays dispersed homogeneously in the form of individual
layers within the polymer matrix, or might be suggestive of the
preferred orientation effect. Therefore, the absence of a
diffraction peak could not be taken as proof for the formation of
an exfoliated nanocomposite, and additional evidence based on
transmission electron microscopy was required.
Thermal stability of the nanoclays was investigated under
nitrogen conditions. Thermogravimetric analysis (TGA) and
derivative thermogravimetric analysis (DTG) results of clay-Na+,
clay-CD and clay-P]O are shown in Fig. 4. Compared to
the thermal stability of clay-Na+, the modied clays (clay-CD,
Fig. 1 1H NMR spectra of CD-DB-N+.
Fig. 3 XRD of the clay-Na+, clay-CD, clay-P]O, BPA and different
Fig. 2 The structure of b-cyclodextrin (b-CD).
BPA/organoclay nanocomposites.
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Fig. 4 TGA and DTG results of the clay-Na+, clay-CD, clay-P]O in
nitrogen conditions (heating rate: 10 ꢀC minꢂ1).
Fig. 5 Low magnification and high magnification TEM images of the
nanocomposites: (a) BPAPO 2 and (b) BPACD 2.
clay-P]O) showed relatively low initial decomposition
ꢀ
temperatures. Additionally, their char residues at 700 C were
very ꢀdifferent. For clay-Na+, the weight loss between 450 and
700 C corresponded to the condensation of silanol groups in
the clay; however, for the modied clays, the weight loss
between these temperatures was caused by the thermal degra-
dation of the intercalated modiers. As shown in Fig. 4, the char
residue of clay-Na+ was 94.1 wt%, while the char residues of
clay-CD and clay-P]O were 77.4 wt% and 81.2 wt%, respec-
tively. Therefore, if char formation of the organomodiers at
700 ꢀC is ignored, the amount of organomodiers in clay-CD
and clay-P]O are 16.7 wt% and 12.9 wt%, respectively.
3.2.2 Morphology of the nanocomposites. Transmission
electron microscopy presented an actual image of clay platelets
to permit identication of the internal morphology of the
nanocomposites. This served as a complement to XRD, espe-
cially when peaks were not observed in the diffraction patterns.
To observe the morphological structure of the bio-based PA
nanocomposites, TEM (at both low and high magnication for
the composition containing 2.0 wt% of the organoclays) was
carried out. In Fig. 5, a display of BPA nanocomposites based on
both the organoclays shows a non-homogeneous distribution in
some orientations. Aggregation of the organoclay also was
observed. In the case of BPACD 2, some exfoliated nanolayers
were found in the polymer matrix, and its agglomeration
behaviors were slightly better than those of BPAPO 2. Since BPA
nanocomposites did not form full exfoliated structures in either
BPACD or BPAPO, how do we explain the fact that no reection
peaks of BPA nanocomposites are indicated in the XRD
measurements? The reason for this might correspond to the
thickness of the BPA nanocomposite specimens. We noticed
that the thickness of each BPA nanocomposite specimen used
in this study was only around 50 mm, which might be too thin to
form an effective reection.
Fig. 6 TGA and DTG curves of BPA and the nanocomposites.
and derivative thermogravimetric analysis (DTG). Fig. 6 shows
TGA and DTG curves of the samples, and corresponding data
are illustrated in Table 1. The neat BPA showed initial weight
loss below 200 ꢀC due to the removal of moisture and some
small organic compounds. The DTG curve indicated that the
neat BPA exhibited two decomposition steps with maximum
decomposition temperatures at 168 ꢀC and 409 ꢀC, respectively.
Aer adding clay-P]O and clay-CD, the nanocomposites were
more stable than BPA, showing signicant increases at the 5
wt% weight loss temperature (T5) and the 10 wt% weight loss
temperature (T10). T5 and T10 of all the nanocomposites were
higher than those of the neat BPA. Considering the TGA and
DTG curves of nanocomposites, we nd that the organoclays
had a signicant effect on the thermal degradation process of
BPA. The thermal stability of the nanocomposites increased due
to the higher barrier/shielding effect resulting from the clay
content in the matrix polymer. Both of the organoclays dis-
played excellent barrier effects to prevent thermal degradation
3.2.3 Thermal properties of the nanocomposites. Thermal
stability is a very important factor for polymeric materials, and
normally this is indicated by thermogravimetric analysis (TGA)
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Table 1 Thermal property data of the samples
Chard yield
Tg
a
b
c
e
Samples
Tinitial (ꢀC)
T10 (ꢀC)
Tmax1 (ꢀC)
Tmax2 (ꢀC)
BPA
153
188
195
192
194
195
236
246
233
243
168
205
205
223
205
409
444
447
439
439
58.3
59.8
60.5
58.1
60.2
130
165
138
133
148
BPACD 2
BPACD 4
BPAPO 2
BPAPO 4
a
b
Temperature at which 5% weight lossꢂw1as recorded by TGA at a heating rate of 10 ꢀC minꢂ1
. Temperature at which 10% weight loss was recorded
c
d
by TGA at a heating rate of 10 ꢀC min
. Maximum decomposition temperatures. Weight percentage of material le aer TGA analysis at a
maximum temperature of 800 ꢀC. e Glass transition temperature recorded at a heating rate of 10 ꢀC minꢂ1 in a nitrogen atmosphere.
of polymer chains at relatively low temperatures. The clay layers
present in the BPA matrix restricted the diffusion of heat to its
bulk, and thus delayed the degradation process. Upon inspec-
tion of the char residues of the samples at 800 ꢀC, we note that
overall, the nanocomposites slightly improved the char residue
at high temperature.
The glass transition temperature (Tg) of the neat BPA and the
nanocomposites were investigated using differential scanning
calorimetry (DSC), and the results are given in Table 1. The rst
heating run of DSC was ignored due to the inuence of thermal
annealing history, and thermal properties were evaluated
according to the DSC curves of the second heating (Fig. 7). It was
found that addition of the nanoclays caused an increase in the
Tg. This suggests that movement of the BPA chains is restricted
by the layers of organoclay, thereby increasing the Tg values of
the nanocomposites. Among the two types of organoclay with
different loading, BPACD 2 gave the greatest increase in Tg value
(Tg ¼ 165 ꢀC) compared to neat BPA. The order of the Tg of
Fig. 8 Flammability of BPA and its nanocomposites by MCC.
the nanocomposites was BPACD 2 > BPAPO 4 > BPACD 4 >
BPAPO 2 > BPA.
3.2.4 Flammability of polymer nanocomposites investi-
gated by MCC. Microscale combustion calorimetry (MCC) was
used to study the ammability of BPA and the nanocomposites
and the total heat release (THR) (given by integration of the
HRR curve). From Table 2, it may be seen that neat BPA had a
peak HRR value (pHRR) of 47.6 W gꢂ1 and a THR value of 14.7 kJ
(Fig. 8). The parameters measured from MCC were heat release
gꢂ1. In comparison, by introducing 2 wt% of clay-CD, the pHRR
rate (HRR) (calculated from oxygen depletion measurements),
and THR values of BPACD 2 decreased greatly. When the
loading of clay-CD was increased to 4 wt%, the pHRR and THR
values of BPACD 4 were further reduced to 42.1 W gꢂ1 and 11.4
kJ gꢂ1, respectively. For the nanocomposites based on clay-P]
O, both BPAPO 2 and BPAPO 4 exhibited even lower pHRR and
THR values, indicating that the improvement of ame retard-
ancy in this system was not completely due to the char yield (see
Table 2). The decreased pHRR and THR with a small amount of
clay-P]O was attributed to compounds with low volatility
released during the degradation procedure. The best pHRR and
THR values were obtained by adding 4 wt% clay-P]O (pHRR ¼
38.9 W gꢂ1 and THR ¼ 8.6 kJ gꢂ1). In addition to the impact of
Table 2 Data recorded in MCC measurements
Samples
BPA
BPACD 2 BPACD 4 BPAPO 2
BPAPO 4
pHRR (W gꢂ1
)
47.6 43.3
14.7 12.4
42.1
11.4
40.2
9.4
38.9
8.6
THR (kJ gꢂ1
)
Fig. 7 DSC curves of BPA and the nanocomposites.
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Table 3 Mechanical properties of BPA and its nanocomposites
Modulus [GPa]
(3 0.1–0.2%)
Maximum stress
sm [MPa]
Strain at sm
3m [%]
Tensile strength
at break sb [MPa]
Strain at sb
3b [%]
Work to fracture
Samples
W [MJ mꢂ3
]
BPA
2.2 ꢃ 0.1
2.1 ꢃ 0.1
2.6 ꢃ 0.1
2.1 ꢃ 0.1
3.0 ꢃ 0.2
59.4 ꢃ 6.5
58.2 ꢃ 6.2
61.4 ꢃ 4.1
62.8 ꢃ 3.5
69.5 ꢃ 6.6
3.6 ꢃ 0.5
3.7 ꢃ 0.5
3.2 ꢃ 0.4
4.1 ꢃ 0.3
3.3 ꢃ 0.4
54.6 ꢃ 5.5
58.0 ꢃ 6.0
61.3 ꢃ 4.1
62.6 ꢃ 3.5
69.5 ꢃ 6.5
4.0 ꢃ 0.8
3.7 ꢃ 0.6
3.2 ꢃ 0.4
4.1 ꢃ 0.3
3.3 ꢃ 0.5
1.5 ꢃ 0.4
1.3 ꢃ 0.4
1.2 ꢃ 0.2
1.5 ꢃ 0.2
1.4 ꢃ 0.3
BPACD 2
BPACD 4
BPAPO 2
BPAPO 4
char residues (condensed phase mechanism) on the ame formation of a non-homogeneous distribution in some orien-
retardancy of BPACD and BPAPO, another ame retardant tations of the nanocomposites. Thermal stability of BPA nano-
mechanism might be possible. The phosphine oxide moieties in composites was improved compared with neat BPA, and in
the clay-P]O might release some phosphorus-containing particular, clay-CD based nanocomposites showed more
radicals which can capture the Hc and HOc in the gas phase, so improvements. The improvement in thermal stability of BPA
that the ammability of BPA nanocomposites remains low. This nanocomposites was attributed primarily to the physical barrier
would explain why the ammability of BPAPO was always lower effect of the organoclays. Flammability of the BPA nano-
than that of BPACD.
composites with different nanoclay concentrations was inves-
3.2.5 Mechanical properties. Mechanical property data for tigated by microscale combustion calorimetry (MCC). It was
neat BPA and the nanocomposites are given in Table 3. The found that clay-P]O had the best effect on improving the ame
nanocomposites were found to be much stiffer than the neat retardancy of BPA, showing the lowest values of peak heat
polymer, and the elastic modulus increased with increasing release rate (pHRR) and total heat release (THR) of the BPA
loading of the organoclays. In the BPACD system, the elastic nanocomposites. With the increase of clay-P]O loading, the
modulus was higher than that of the neat PA and the elastic BPA nanocomposites showed improved ame retardancy. In the
modulus increased with increasing loading of clay-CD. The case of clay-CD based nanocomposites, mechanical properties
maximum modulus value was observed with 4 wt% of clay-P]O and ame retardancy of BPACD also increased with the increase
in the BPA matrix, providing more stiffness to the materials of nanoclay loading. In comparison, clay-P]O based nano-
(stiffness being a function of the aspect ratio). Such improve- composites showed even greater improvements in ame
ment of the mechanical properties of BPAPO may be attributed retardancy and mechanical properties. Besides the char residue
to the extensive interaction (via formation of hydrogen bonding) impact on ame retardancy of both BPACD and BPAPO, another
between the triamine TAP modier in BPAPO and the BPA possible ame retardant mechanism for BPAPO involves phos-
chains. The results also indicate signicant increase in tensile phine oxide moieties in the clay-P]O releasing some phos-
strength of BPAPO and BPACD, compared with that of the neat phorus-containing radicals which can capture the Hc and HOc
BPA. The incorporation of these functional organoclays into the in the gas phase, so that the ammability of BPA nano-
polymer chains can reinforce the polymer, giving the observed composites remains low. Here, we have systematically investi-
increase in this important property. When using conventional gated and described the effects of functional organoclays on
modied nanoclay (Cloisite 30B), mechanical properties of BPA ammability, thermal and mechanical properties of BPA
nanocomposites (e.g. tensile strength at break) are severely nanocomposites. Our ndings strongly suggest that these
decreased.22 Intimate blending of the two phases, presumably sustainable biobased semi-aromatic polyamide/functional clay
with chemical bonding between them, provides a combination nanocomposites have great potential for being used to develop
of some of the best properties of the two components.27 The high performance materials in different areas.
maximum stress at break (ultimate strength) was found to
increase initially with increase in clay-P]O content, and at 4
wt% organoclay, showed a maximum value of 69.5 MPa. Rela-
Acknowledgements
tive to the corresponding 59.4 MPa value for neat BPA, this
represents signicant enhancement.
This research is partly funded by the European Commission
under the 7th Framework Programme (Marie Curie Career
´
Integration Grant) and Ramon y Cajal grant.
4. Conclusions
Notes and references
Since design and selection of functional nanoclays are very
important for preparing polymer nanocomposites, two novel
organoclays containing modied phosphine oxide (TAP) and
functional b-CD were synthesized via ion-exchange reaction.
Two types of BPA nanocomposites, BPACD and BPAPO, were
produced by solution blending. TEM results indicated the
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