Studies on mechanical, thermal and dynamic mechanical properties of functionalized nanoalumina reinforced sulphone ether linked tetraglycidyl epoxy nanocomposites

Article abstract of DOI:10.1039/c4ra06511e

The objective of the present work is to synthesize 1,4′-bis (4-amine-phenoxy) sulphone benzene epoxy resin (TGBAPSB) via 1,4′-bis (4-amine-phenoxy) sulphone benzene (BAPSB) and epichlorohydrin in order to obtain tetra functional epoxy with improved properties. The molecular structure of TGBAPSB epoxy resin was confirmed from FTIR and NMR spectral data and molecular weight was determined by GPC and epoxy equivalent weight (EEW) by titration method. The amino functionalized nanoalumina (F-nAl) was synthesized via the sol-gel method using 3-aminopropyltriethoxysilane and has been confirmed by FT-IR. TGBAPSB epoxy resin was further reinforced with varying weight percentages (1-5 wt%) of F-nAl and cured with diaminodiphenylmethane (DDM). The thermal and thermo-mechanical behaviour of TGBAPSB epoxy matrix and nanocomposites were analysed by TGA, DMA and DSC. The surface morphology of the epoxy nanocomposites was examined using XRD, TEM, SEM and AFM studies. Data obtained from mechanical, thermal and thermo-mechanical, dielectric and water absorption studies indicate a significant improvement in properties of the resultant epoxy nanocomposites, which appear to be ideal material for advanced high performance applications when compared to those of neat epoxy matrices. This journal is

Full text of DOI:10.1039/c4ra06511e

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PAPER
Studies on mechanical, thermal and dynamic
mechanical properties of functionalized
nanoalumina reinforced sulphone ether linked
tetraglycidyl epoxy nanocomposites†
Cite this: RSC Adv., 2014, 4, 40132
a
b
a
*
D. Duraibabu, M. Alagar and S. Ananda Kumar
The objective of the present work is to synthesize 1,40-bis (4-amine-phenoxy) sulphone benzene epoxy
resin (TGBAPSB) via 1,40-bis (4-amine-phenoxy) sulphone benzene (BAPSB) and epichlorohydrin in order
to obtain tetra functional epoxy with improved properties. The molecular structure of TGBAPSB epoxy
resin was confirmed from FTIR and NMR spectral data and molecular weight was determined by GPC
and epoxy equivalent weight (EEW) by titration method. The amino functionalized nanoalumina (F-nAl)
was synthesized via the sol–gel method using 3-aminopropyltriethoxysilane and has been confirmed by
FT-IR. TGBAPSB epoxy resin was further reinforced with varying weight percentages (1–5 wt%) of F-nAl
and cured with diaminodiphenylmethane (DDM). The thermal and thermo-mechanical behaviour of
TGBAPSB epoxy matrix and nanocomposites were analysed by TGA, DMA and DSC. The surface
morphology of the epoxy nanocomposites was examined using XRD, TEM, SEM and AFM studies. Data
obtained from mechanical, thermal and thermo-mechanical, dielectric and water absorption studies
indicate a significant improvement in properties of the resultant epoxy nanocomposites, which appear to
be ideal material for advanced high performance applications when compared to those of neat epoxy
matrices.
Received 1st July 2014
Accepted 19th August 2014
DOI: 10.1039/c4ra06511e
www.rsc.org/advances
methods seems to have improved the toughness of epoxies
without the loss of rigidity.4–9 Quite recently, epoxy resins have
1. Introduction
been modied with materials having rigid and so skeleton in
order to have both toughness and stiffness that are ideally
required for high performance applications.10–13 It has also been
reported that the toughness of tetra functional epoxy resin can
be improved without a signicant loss of stiffness by skeletal
modication through the incorporation of specic atoms and
groups into their backbone in order to meet the required high
performance characteristics mentioned above. Though the
literature describes a variety of epoxy resins and their nano-
composites, there is still a need for high performance tetragly-
cidyl epoxy resins having stiffness and toughness and their
demand is increasing day by day. Hence, structural modica-
tion of epoxy resins along with suitable nanoreinforcements to
achieve enhanced thermal and thermo mechanical properties is
required for high performance industrial applications.14–17
Introduction of sulphur group in to epoxy resins offers excellent
thermal stability, high moisture resistance, low ionic contami-
nant concentration, and good dielectric properties. The addi-
tion of inorganic nanoparticles, carbon nanotubes and carbon
akes are the widely used as nanometric reinforcements for
epoxy matrices to enhance their mechanical behavior.18
However, it has been reported recently that alumina nano-
particles emerged as potential nanoreinforcement for an
The characteristics of tetra glycidyl epoxy resins constitute an
excellent combination of chemical and corrosion resistance,
and good mechanical and electrical properties. These charac-
teristics, along with a long service life, make epoxies a necessity
in the future growth of new technologies. Presently, there is
high potential for more sophisticated application of tetra
functional epoxies in both the automotive and aerospace
industries. However, these epoxies have brittle characteristics
that prevent their use in such potential applications in the
aerospace and automotive industries. For example, epoxy resins
tend to be either brittle or notch sensitive for structural appli-
cations. Therefore, tremendous efforts have been focused on
improving the toughness of epoxy systems, which has stimu-
lated an overwhelming interest in the recent decades.1–3
Toughening can be achieved either by reduction of cross-link
density or by the use of liquid rubbers and plasticizers leading
to an increased plastic deformation. However, none of these
aDepartment of Chemistry, Anna University, Chennai 600025, India. E-mail:
sri_anand_72@yahoo.com; Fax: +91-44-22200660; Tel: +91- 44-22358661
bDepartment of Chemical Engineering, Anna University, Chennai 600025, India
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra06511e
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advanced composite insulation materials when compared to solution and ltered to get a yellow colour solid product, which
that of micron size lled alumina powder.19 Therefore the was recrystallized from ethanol. BNPSB (0.20 mol), 0.78 g Pd/C
development of novel skeletal modied tetraglycidyl epoxy and 600 ml ethanol were introduced into a 1000 ml three-neck
resins having both toughness and stiffness is a major goal in the ask to which hydrazine hydrate (80 wt%) was added in drop-
eld today. To achieve both toughness and stiffness to a greater wise over a period of 1 h at reux temperature and the reaction
extent, tetra functional epoxy resin is skeletally modied with continued for about 5 h. The product BAPSB obtained was
sulphone moiety and subsequently reinforced with optimum puried and preserved for further use.20 The sequence of reac-
percentage of functionalized inorganic nanomaterial (F-nAl) tions involved is illustrated in Scheme 1.
and cured with DDM. Hence an attempt to achieve the above
said objectives is reported here with supporting evidences.
2.3 Synthesis TGBAPSB epoxy resin
Tetraglycidyl 1,4’-bis(4-amine-phenoxy) sulphone benzene
2. Experimental
2.1 Materials
(TGBAPSB) resin was synthesized using EPC and BAPSB with
40% NaOH solution.20 A pale brown coloured resin TGBAPSB
obtained (yield 80%) was puried and preserved for further use
(Scheme 1).
All chemicals were used without further purication except
dimethylformamide (DMF) which was puried by distillation
under reduced pressure over calcium hydride. p-Chloroni-
2.4 Amino functionalized nano alumina
trobenzene, potassium carbonate, absolute ethanol, hydrazine
ꢀ
hydrate (80 wt% water solution), epichlorohydrin (EPC),
benzene, tetrahydrofuran (THF), 10% palladium (Pd/C) on
activated carbon, pyridine, hydrochloride (HCl), phenolphtha-
lein, dimethylbenzene and sodium hydroxide were obtained
from SD Fine Chemical Company, India. Alumina nano-
particles, di-hydroxy diphenylsulphone and 3-amino-
propyltriethoxysilane (APTES) were purchased from Sigma
Aldrich, India. 4, 40-Diaminodiphenylmethane (DDM) was
obtained from Huntsman, USA.
Al2O3 nanoparticles were dried in a vacuum oven at 180 C for
24 h to remove the moisture adsorbed on the surface. 4 g of
Al2O3 nanoparticles and an appropriate amount of 3-amino-
propyltriethoxysilane (4.4 g) were added into a 500 ml three-
neck ask, equipped with a mechanical stirrer and a reux
condenser, and are mixed in high purity dimethylbenzene by
stirring at 110–120 ꢀC for at least 4 h. Aer ltration, the APTES
functionalized Al2O3 nanoparticles were washed several times
with dimethylbenzene to remove the unreacted silane moieties
and dried in a vacuum oven at 120 ꢀC for 2 h to remove the
residual solvent.21 The sequence of reactions involved is illus-
trated in Scheme 2.
2.2 Synthesis of (4-nitro-phenoxy)sulphone benzene
(BNPSB) and (4-amine-phenoxy)sulphone benzene (BAPSB)
BNPSB was synthesized by the reaction of di-hydroxy diphenyl-
sulphone (0.20 mol) and p-chloro nitrobenzene (0.44 mol) in
DMF (300 ml) in the presence of potassium carbonate (0.44
2.5 Preparation of surface-modied nanoalumina reinforced
epoxy nanocomposites
mol). The reactants were heated to 145–150 ꢀC for 8–10 h under The TGBAPSB epoxy resin and the desired amount of 1, 3 and 5
N2 atmosphere. Aer being cooled to room temperature, the wt% of amino functionalized nanoalumina were mechanically
resulting product was poured into a water/ethanol (1/1, v/v) stirred at 50 ꢀC for 24 h. A stoichiometric amount of DDM,
Scheme 1 Synthesis of TGBAPSB epoxy resin.
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(Model DMS-6000 Japan) in a three point bending congura-
ꢀ
tion, at a temperature range of 30 to 250 C using a specimen
with the dimension of 55 mm ꢁ 10 mm ꢁ 3 mm. The frequency
used with 1.0 Hz at rate is 2 ꢀC minꢂ1 for cure epoxy nano-
composites. The instrument measured the storage modulus (E0)
and dumping (tan d) of the specimen under on oscillatory load
as a function of temperature. The temperature corresponding to
the maximum in tan d versus temperature plots was recorded as
the measurement of glass transition temperature (Tg). Thermo
gravimetric analysis of composites was carried out using TGA –
Thermal Analyst NETZSCH STA 409 PC (TA instruments USA) at
a heating rate of 10ꢀC minꢂ1 from 0 ꢀC to 700 ꢀC under a
continuous ow of N2 atmosphere (60 ml minꢂ1) to determine
thermal degradation temperature, percentage weight loss and
char yield formation. The instrument was calibrated with
calcium oxalate and aluminum supplied by NETZSCH. About 50
mg of samples was taken for each analysis. X-ray diffraction
(XRD) studies of the samples were carried out using a Rich
Saifert-3000. X-ray diffractometer CuKa radiation with a copper
Scheme 2 Amino functionalized nanoalumina.
corresponding to epoxy equivalents was also added (Table S1†).
The resulting product was poꢀured into a preheated mould. The
mould was preheated at 120 C for 1 h to remove the moisture
and trapped air. The samples were cured successively at 120 ꢀC
for 2 h, post-cured at 180 ꢀC for 3 h and nally the cured sample
was removed from the mould and characterized. The func-
tionalized nanoalumina (F-nAl) forms a covalent bond with
TGBAPSB epoxy resin as shown in Scheme 3.
2.6 Characterization
ꢀ
˚
target (l 1.5405 A) over the 2q range of 10–70 at a scanning rate
of 0.04ꢀ minꢂ1. A JEOL JSM-6360 Scanning electron microscope
(SEM) was used for the sample analysis and the fractured
samples were prepared by coating gold on the surface of the
samples and analyzed further. A JEOL JEM-3010 analytical
transmission electron microscope (TEM), operating at 300 kV
with a measured point-to-point resolution of 0.23 nm, was used
to characterize the phase morphology of the polymers. TEM
samples were prepared by dissolving polymers in DMF mounted
on carbon-coated Cu TEM grids and dried 24 h at room
FT-IR spectra were recorded on a Perkin Elmer 781 FTIR spec-
trometer to determine the chemical structure of TGBAPSB epoxy
resin. The spectrum of TGBAPSB epoxy resin cured with DDM
was obtained by the following method. A small portion of the
cured epoxy matrix was ground to a ne powder, mixed with KBr
powder, and pressed into a pellet which is used to obtain the
1
spectrum. H and 13C NMR spectra were recorded on a Bruker
400 MHz NMR spectrometer with CDCl3 as the solvent as
internal reference and TMS as external reference. The dynamic
mechanical analysis was carried out on SII Nanotechnology
Scheme 3 The reaction mechanism of TGBAPSB with F-nAl nanoparticle.
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temperature (RT) to form a lm in <100 nm size. The surface machine so that they are cantilevered upward. The pendulum
topology of the fractured surface was investigated by means of was released and the force consumed in breaking the sample
AFM Seiko SPI3800N, series SPA-400 (Tokyo, Japan). The surface calculated from the height the pendulum reached on the ow
roughness of the samples was analyzed. The dielectric constant through. The test specimen was prepared by matching opera-
measurements were carried out with help of impedance analy- tion. Five specimens were tested for each sample.
ser (Solartron impedance/gain phase analyser 1260) at room
temperature (RT) using platinum (Pt) electrode at 30 ꢀC at a
2.10 Water absorption studies
frequency range of 1 MHz. This experiment was repeated four
The water absorption measurements of tetra glycidyl epoxy
times under same condition.
resin were carried out according to ASTM D570-81 was
immersed in water for 24 h at 25 ꢀC and the percentage of water
absorbed by the specimen was calculated using the following
2.7 Gel permeation of chromatography
ꢀ
The number average molecular weight (Mn), weight average
eqn (2).
ꢀ
ꢀ
ꢀ
molecular weight (Mw) and polydispersity index (Mw/Mn) of the
epoxy samples were determined with Waters 501 gel permeation
chromatography equipped with three ultra styragel columns
and a differential refractive index (RI-401) detector. The
molecular weights were calibrated against polystyrene stan-
dards using tetrahydrofuran as mobile phase.
% water absorption ¼ (W2 ꢂ W1) ꢁ 100/W1
(2)
where, W1 is the initial weight of the sample and W2 is the
weight of the sample aer immersion in water for 24 h at 25 ꢀC.
3. Results and discussion
2.8 Determination of the epoxy equivalent weight (EEW) of
the tetra glycidyl epoxy resin
FT-IR spectra were used to elucidate the functional groups
present in the TGBAPSB epoxy resin before and aer rein-
forcement with F-nAl. FT-IR spectrum of functionalized F-nAl is
shown in Fig. S1.† The absorption peak at 3362 cmꢂ1 was
attributed to NH2 groups. The peaks at 2919 and 2844 cmꢂ1
were assigned to the symmetric methylene (CH2) stretching
vibrations respectively. The presence of bands at 1580 cmꢂ1
(NH), 1417 cmꢂ1 (CH) and 1148 cmꢂ1 (C–N) are due to
stretching and bending vibrations. The FTIR spectra of BNPSB
and BAPSB is presented in Fig. S2.† The appearance of bands at
2836 cmꢂ1 (Ar-CH), 1586 cmꢂ1 (C]C), 1491 cmꢂ1 (C–O–C), 1153
cmꢂ1 (Ar-NO2), 1322 cmꢂ1 (S]O), 741 cmꢂ1 (C–S) and 842 cmꢂ1
(C–N). The disappearance of nitro group at 1153 cmꢂ1 and
The EEW determination was performed using the pyridine/
hydrochloride titration method and the experimental result
obtained was 176 (g per eq.) which is close to the theoretical
value of 164 (g per eq.). About 2 to 3 g of the TGBAPSB epoxy
resin was weighed in a 250 ml round bottom ask. 25 ml of 0.2
N pyridinium chloride (4 ml of concentration hydrochloric acid
in 246 ml of pyridine) was added. The ask was then gently
heated and reuxed for 30 min continuously and cooled. Then
0.1 N of methanol and a few drops of phenolphthalein were
added, titrated against 0.2 N NaOH. Blank titration was also
carried out. The EEW value of the tetra glycidyl compound was
determined using the following eqn (1)
EEW ¼ (10 000 W)/(f(B ꢂ S))
(1)
where, W ¼ the weight of tetra glycidyl epoxy resin (g), f ¼ the
calibration factor for NaOH solution, B ¼ the amount of NaOH
solution for blank test (ml), S ¼ the amount of NaOH solution
for tetra glycidyl epoxy resin sample (ml).
2.9 Mechanical properties
The tensile, (stress–strain) properties were determined using
INSTRON (Model 6025 UK) as per ASTM D 3039 at 10 mm minꢂ1
cross-head speed using specimen with a width of 25 mm, length
of 200 mm, and thickness of 3 mm. A distance of 115 mm was
kept in between the grips. The exural (strength and modulus)
properties were measured (INSTRON, Model 6025 UK) as per
ASTM D 790 using specimen with dimensions 3 mm in depth,
10 mm in width, and 90 mm in length at 10 mm minꢂ1 cross-
head speed. The unnotched Izod impact strength of each
sample was studied as per ASTM D 256-88. All samples were
tested unnotched so that they would be more sensitive to the
transitions between ductility and brittleness. Specimens,
having a thickness of 3.2 mm with 10 mm cross section and 64
Fig. 1 FT-IR spectra of (a) TGBAPSB epoxy resin (b) TGBAPSB epoxy
mm length were clamped in the base of the pendulum testing resin cured with DDM.
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appearance of peak at 3475 cmꢂ1 due to NH2 are also shown in
Fig. S2(a) and (b).† In Fig. 1a, the band at 912 cmꢂ1 appears due
to the presence of oxirane ring. The bands appeared at 2975
cmꢂ1 and 1650 cmꢂ1 represent the aromatic ring of TGBAPSB
and 821 cmꢂ1 for the C–N stretching of TGBAPSB. The disap-
pearance of peak at 912 cmꢂ1 and appearance of peak at 3340
cmꢂ1 represent the opening of oxirane ring and formation of
secondary hydroxyl group respectively. Fig. 1(b) conrms the
reaction occurred between epoxy and DDM. Having elucidated
the functional groups, it is a requisite to understand the
structural characteristics of the synthesized TGBAPSB epoxy
1
resin. Therefore, HNMR was employed to interpret the chem-
ical structure of TGBAPSB epoxy resin. Fig. S4† illustrates
1HNMR spectrum of BNPSB. The appearance of chemical shis
at around (m, 16H, ArH) 6.5–7.9 ppm, conrmed the presence
of aromatic protons. Fig. S5† shows the 13CNMR spectrum of
BNPSB. The peaks at 144, 114, 123, 162, 163, 117, 130 and 134
ppm (C aromatic) are assigned to the aromatic carbons of
BNPSB. Fig. S6† illustrates the 1HNMR spectrum of BAPSB. The
appearance of chemical shis around 6.5–7.9 ppm (m, 16H,
ArH) conrmed the presence of aromatic protons and the
appearance of di-amine chemical shis occurred at (s, 4H,
ArNH2) 3.9 ppm. Fig. S7† shows the 13CNMR spectrum of
BAPSB. The peaks at 143, 123, 116, 147, 164, 114, 130 and 135
ppm (C aromatic) are assigned to the aromatic carbons of
Fig. 2 Mechanical properties of neat (TGBAPSB) and F-nAl epoxy
nanocomposites.
impact strength and are shown in Fig. 2. For instance, the
values of tensile, exural and impact strength of system ‘c’ (3
wt%) are 124.5 MPa, 212.5 MPa and 238.4 J mꢂ1 respectively,
when compared to those of neat TGBAPSB (system ‘a’). This may
be due to the formation of strong covalent bond between epoxy
and F-nAl nanoparticles through silane linkage. Similar obser-
vation was made by Laura et al. (2008) for mechanical, and
fracture properties of alumina based epoxy nanocomposites.22
In the case of higher concentration loaded F-nAl (5 wt%) rein-
forced nanocomposite system ‘d’, the mechanical properties
were found to be decreased. This could be attributed to the
irregular dispersion of the alumina nanoparticles within the
epoxy matrix thereby creating a void of cross-linking. This void
of crosslinking paves an avenue for the molecular relaxation
and consecutive segmental mobility of the polymer chains. This
is well supported by the value of Tg observed for the system ‘d’
from the DMA analysis. This may be considered as one of the
reasons for the decrease in mechanical properties of the 5 wt%
(system ‘d’) F-nAl nanocomposites. Similar phenomenon was
reported by Mohanty et al. (2013) for aggregation resulting from
high loading of alumina in epoxy nanocomposites.23 The
increasing and decreasing trend of values of mechanical prop-
erties with respect to nanoreinforcement loading may also be
attributed to the uniform and irregular dispersion the F-nAl in
the TGBAPSB epoxy matrices. This could be correlated with the
SEM analysis observations, which clearly indicate that the
surface roughness increases at higher loading of F-nAl into the
TGBAPSB epoxy system ‘d’ which exhibits irregular dispersion.
Thus, it could be concluded that the mechanical properties of
systems ‘b’ and ‘c’ having proper distribution of F-nAl which is
brought about only at a lower loading of F-nAl namely 1 and 3
wt% exhibit an increasing trend.
1
BAPSB. Fig. S8† illustrates the HNMR spectrum of TGBAPSB
epoxy resin. The chemical shi values obtained are assigned
according to the protons of their environment; 6.5–7.9 ppm (m,
16H, ArH) indicating the presence of aromatic protons. The
remaining methyl, oxirane, and methylene protons appear at
around 2.5 (s, 8H, CH2), 3.2–3.7 ppm (d, 12H, CH2) respectively.
Fig. S9† depicts the 13CNMR spectrum of TGBAPSB. The
appearance of signals respectively at d ¼ 45 ppm and 50 ppm are
assigned due to the presence of –OCH2 and –CH– of TGBAPSB
epoxy resin. The signal at d ¼ 59–60 ppm is assigned to the
presence of –N–CH2 carbon. The remaining signals that appear
respectively at 109, 116, 127, 144, 148 and 165 ppm (C aromatic)
are assigned to the aromatic carbons of TGBAPSB. Fig. S10†
shows the GPC graph of TGBAPSB epoxy with a number average
ꢀ
molecular weight (Mn) 775, weight average molecular weight
ꢀ
ꢀ
ꢀ
(Mw) 813 and poly dispersity index (Mw/Mn) 1.04.
3.1 Mechanical properties
The nanocomposites are expected to possess improved tough-
ness, better mechanical properties than the neat TGBAPSB
epoxy resin. The improvement in mechanical properties was
ascertained analyzing the tensile strength, exural strength and
impact strength of neat and nanocomposites. The values of
tensile strength, exural strength and impact strength of neat
and nanocomposites are presented in Table S2.† A signicant
enhancement in tensile strength, exural strength and impact
3.2 Dynamic mechanical analysis
strength was observed when F-nAl was introduced into the The results of DMA of TGBAPSB (neat) epoxy resin and (1–5
epoxy matrix. It was also interesting to note that the 1 wt% wt%) F-nAl reinforced TGBAPSB epoxy nanocomposites are
(system ‘b’) and 3 wt% (system ‘c’) of F-nAl reinforced nano- shown in Fig. 3 and Table S3.† It can be observed that the
composites systems exhibited the ideal values of mechanical storage modulus (E0) increases for nanocomposites systems ‘b’
properties in terms of tensile strength, exural strength and and ‘c’, which is higher than that of the neat TGBAPSB epoxy
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Fig.
3 Storage modulus of neat (TGBAPSB) and F-nAl epoxy
nanocomposites.
Fig. 4 Tan d of neat (TGBAPSB) and F-nAl epoxy nanocomposites.
system ‘a’. However, the maximum improvement in storage
modulus is observed for nanocomposites up to 3 wt% of F-nAl
system ‘c’. The nanocomposites system ‘d’ has exhibited a least
value of storage modulus when compared to that of nano-
composites systems ‘b’ and ‘c’. The increase in storage modulus
observed upto 3 wt% of all F-nAl reinforced systems ‘b’ and ‘c’
may be due to the uniform dispersion of nanoalumina particles
within the epoxy matrix.23 During the curing process, the DDM
reacts with epoxy and F-nAl forming covalent bond between
reinforcement and matrices. The decrease in storage modulus
observed for system ‘d’ (beyond 3 wt% of F-nAl loading) is
mainly attributed to irregularly dispersed F-nAl particles into
the epoxy matrix and in turn the void of cross-linking is
increased. Hence the segmental mobility rises, which leads to
the decrease of the storage modulus. On the other hand, the
neat TGBAPSB (system ‘a’) showed the least value of storage
modulus (3.2 GPa) among all the systems ‘b’ and ‘c’. This may
be due to the presence of exible ether and sulphone linkages of
TGBAPSB epoxy resin.24 The increase in storage modulus up to 3
wt% loading of F-nAl TGBAPSB epoxy nanocomposites may also
be attributed to the homogenous dispersion of F-nAl in the
epoxy matrix system ‘c’. However, at higher loading of F-nAl (5
wt%), a decreasing trend was observed for system ‘d’, which
could be attributed to the irregular dispersion of F-nAl particles
in the TGBAPSB epoxy matrix. These observations are in
concurrence with those results of mechanical properties of
TGBAPSB epoxy nanocomposites where higher loading of 5 wt%
F-nAl resulted in a negative feedback on the mechanical and
morphological characteristics.
3 wt% of F-nAl incorporation. The increasing Tg observed for ‘b’
and ‘c’ systems may be due to the increase in storage modulus
resulting from the uniform dispersion of alumina nanoparticles
within the epoxy matrix and thus offering stiffening effect with
the presence of alumina and silane components of F-nAl that
tightly holds the TGBAPSB epoxy matrices in a cross-linked
structure by restricting the mobility of epoxy resin chain
segments.25,26 However, the Tg value of system ‘d’, decreases due
to the aggregation of alumina nanoparticles at higher (5 wt%)
concentration of F-nAl.27
3.4 Thermo gravimetric analysis
The thermal degradation behavior of neat and nanocomposites
are presented in Fig. 5 and Table 1. The thermal stability and
char yield TGBAPSB systems are improved up to 3 wt% loading
of nanoreinforcements. For example the initial decomposition
of TGBAPSB system ‘a’ occurred at 330 ꢀC while the initial
decomposition temperatures of system ‘a’ and system ‘b’ shown
in Table 1 were signicantly improved to 337 ꢀC and 349 ꢀC
respectively. Similarly the char yield of system ‘a’ was 16% and
that of the system ‘b’, system ‘c’ were enhanced to 21% and 31%
3.3 Glass transition temperature
Glass transition temperature (Tg) was determined from the peak
position of tan d, which increased from 145 to 203 ꢀC with
increasing nanoalumina content as shown in Fig. 4 and the
values of Tg are given in Table S3.† The Tg of neat TGBAPSB
epoxy resin was found to be the least (145 ꢀC) among all the
systems investigated. It was interesting to note that the Tg of
nanocomposites (systems ‘b’ and ‘c’) increased steadily up to Fig. 5 TGA of neat (TGBAPSB) and F-nAl epoxy nanocomposites.
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Table
1 Data on thermal properties of TGBAPSB epoxy
nanocomposites
TGBAPSB/% Initial decomposition Char yield
System F-nAl
temperature (ꢀC)
(%)
Tg (ꢀC)
A
B
C
D
100/0
100/1
100/3
100/5
330
337
349
345
16
21
31
26
148
189
205
180
respectively. The TGA curve of 3 wt% (system ‘c’) loaded
alumina nanocomposite indicates an improved thermal
stability than that of the 5 wt% (system ‘d’) alumina reinforced
nanocomposites, which showed a reverse trend in stability and
are presented in Fig. 5. This could be attributed to the uniform
dispersion of nanoalumina particles within the nano-
composites. However, the aggregation of higher loading of 5
wt% of nanoalumina leads to reduced thermal stability, which
is indicated by its inferior initial degradation and char yield in
comparison with that of 3 wt% loaded system.23 It was inter-
esting to observe that the increase in weight percentages (1, 3
and 5 wt%) of F-nAl in the TGBAPSB epoxy systems namely ‘b’,
‘c’ and ‘d’, prolonged the initial degradation temperature of the
TGBAPSB nanocomposites when compared to that of neat
TGBAPSB epoxy matrix system ‘a’. This enhancement in
thermal stability could be ascribed to the presence of inorganic
materials like alumina (Al) and silane (Si) components of F-nAl
within the epoxy network.
Fig. 7 XRD spectra of (a) neat (TGBAPSB) (b) TGBAPSB/1 wt% F-nAl, (b)
TGBAPSB/3 wt% F-nAl and (d) TGBAPSB/5 wt% F-nAl epoxy
nanocomposites.
Fig. 8 TEM photographs of systems (a) TGBAPSB/3 wt% F-nAl and (b)
TGBAPSB/5 wt% F-nAl epoxy nanocomposites.
3.5 Differential scanning calorimetry
decreasing Tg value observed for systems ‘b’, ‘c’, ‘d’ and ‘a’ from
both DMA and DSC studies could be mainly due to the uniform
and non-uniform dispersion of F-nAl within the epoxy matrix.
The values of the glass transition temperature (Tg) of neat epoxy
matrix and nanoalumina reinforced nanocomposites were
obtained from the DSC analysis are also presented in Table 1.
The values of Tg of neat TGBAPSB (system ‘a’) was 148 ꢀC
whereas the values of Tg of nanocomposites system ‘b’, system
‘c’ and system ‘d’ are 189 ꢀC, 205 ꢀC and 180 ꢀC respectively
(Fig. 6). These results are in good agreement with the tan d (Tg)
values resulted from DMA studies (Table 1). The increasing and
3.6 XRD and TEM studies
XRD diffraction (XRD) analysis was carried out for the neat
TGBAPSB and epoxy reinforced with different weight percent-
ages of F-nAl and the results are illustrated in Fig. 7. The Fig. 7
depicts the variation in the peak intensity of F-nAl lled
TGBAPSB epoxy nanocomposites from 2q ¼ 16.2ꢀ to 2q ¼ 13.2ꢀ
respectively. It can be clearly seen that the peak intensity
signicantly reduced up to 3 wt% (systems ‘b’ and ‘c’). The shi
towards a lower angle indicates that the interplanar spacing was
decreased and indicating a mixed intercalated and exfoliated
behavior of the epoxy nanocomposites,28,29 when compared to
that of neat TGBAPSB epoxy matrix and are shown in Fig. 7. The
decrease in interplanar spacing was more in the case of system
‘d’ than in other systems namely ‘b’ and ‘c’. This trend clearly
indicates that the systems ‘b’ and ‘c’ have more exfoliated
character than system ‘d’. The introduction of F-nAl at lower
concentrations led to its proper dispersion within the TGBAPSB
epoxy systems ‘b’ and ‘c’ (Fig. 8a) and thus showing more
exfoliation than system ‘d’. However, higher weight percentage
loading (system ‘d’) of nanoalumina particles with epoxy resin
had strong tendency of nanoalumina particles to agglomerate
Fig. 6 DSC of neat (TGBAPSB) and F-nAl epoxy nanocomposites.
40138 | RSC Adv., 2014, 4, 40132–40140
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Table 2 Dielectric properties and water absorption of TGBAPSB epoxy
nanocomposites
within the resin and thus led to a decreased interplanar
spacing.27 The decreased interplanar spacing observed for
system ‘d’ having higher loading of nanoparticles can be
attributed to the inevitable occurrence of aggregates, which was
conrmed by TEM image (Fig. 8(b)).
TGBAPSB/%
F-nAl
Dielectric constant
Water absorption
(%)
System
(30)
A
B
C
D
100/0
100/1
100/3
100/5
4.00
3.85
3.60
3.55
0.067
0.064
0.062
0.061
3.7 Morphology of the nanocomposites
Fig. 9 show the SEM and AFM micrographs of TGBAPSB (neat)
epoxy (system ‘a’) and nanocomposites (systems ‘b’, ‘c’ and ‘d’).
It was observed that the surface of TGBAPSB (neat) epoxy was
smooth (Fig. 9(a)). However, on addition of F-nAl particles, the
surface morphology of the epoxy nanocomposites ‘b’, ‘c’ and ‘d’
was found to be rough in nature and the surface roughness
increases up to 3 wt% of F-nAl concentration. There is an
excellent adhesion due to the formation of chemical bond
between the F-nAl and the epoxy resin and hence, there is a
formation of a partially intercalated and exfoliated structure.
This effect results in improved strength of the nanocomposites
namely ‘b’ and ‘c’ systems (Fig. 9(b) and (c)).30 Furthermore,
addition of 5 wt% of F-nAl reinforced nanocomposites system
‘d’ possesses crack initiation sites due to the presence of
aggregates of F-nAl particles and this eventually results in the
cutback of storage modulus. Similar observations were made
from DMA and mechanical studies where 5 wt% F-nAl
reinforced nanocomposites exhibited depletion in storage
modulus due to the aggregation of excess nanoalumina parti-
cles (Fig. 9(d)).29 Furthermore, the TEM images also support the
observation made from AFM, SEM, DMA and mechanical
studies.
3.8 Dielectric behavior
The values of dielectric constant of neat and nanoalumina
reinforced epoxy composites are shown in Table 2. Dielectric
constant is a property of an electrical insulating material (a
dielectric) equal to the ratio of the capacitance of a capacitor
lled with the given material to the capacitance of an identical
capacitor in a vacuum without the dielectric material. An
excellent insulator should have low dielectric electric constant
values. It was noted that the incorporation of F-nAl in to the
TGBAPSB epoxy reduces the dielectric constant values. The
values of dielectric constant are decreased with an increase in
concentration of F-nAl in the epoxy matrix. For example the
dielectric constant of neat TGBAPSB epoxy matrix system was
4.00, whereas the dielectric constant of epoxy nanocomposites
systems ‘b’, ‘c’ and ‘d’ were 3.85, 3.60 and 3.55 respectively. This
may be attributed to the increased interfacial areas created by
the F-nAl during the formation of nanocomposites. These
results are in concurrence with those reported by Gonon et al.
(2001).31 These results indicate that reinforcing F-nAl, into the
TGBAPSB epoxy matrix increases the insulating property
besides having the better inuencing effect at lower loading and
impact on the insulation properties.
3.9 Water absorption properties
Water absorption properties also followed the same trend as
thermo-mechanical properties where the values decreased with
increasing F-nAl content. The values of water absorption prop-
erties of neat and nanoalumina reinforced epoxy composites are
shown in Table 2. It can be seen from Table 2 that the water
absorption gradually decreased with an increase in the F-nAl
content. For example, the percentage of water absorption of the
system ‘a’ was 0.067, whereas the same for the systems ‘b’, ‘c’
and ‘d’ were found to 0.064, 0.062 and 0.061 respectively. This
could have been caused by two factors. Firstly, the volume of
epoxy for water diffusion is reduced with increasing nano-
particle content. Secondly, the presence of nanoparticles can
increase the path length for moisture diffusion as reported by
Ng et al. (2001).32
Fig. 9 SEM and AFM photographs of systems (a) neat (TGBAPSB) (b)
TGBAPSB/1 wt% F-nAl (c) TGBAPSB/3 wt% F-nAl and (d) TGBAPSB/5
wt% F-nAl epoxy nanocomposites.
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Paper
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Novel skeletally modied sulphone tetra functional epoxy
nanocomposites were successfully developed using TGBAPSB
epoxy resin and surface modied F-nAl. The surface
morphology of the epoxy nanocomposites was investigated by
XRD, TEM, SEM and AFM studies. It was interesting to observe
that the XRD patterns of 1 wt%, 3 wt% and 5 wt% loaded F-nAl
TGBAPSB nanocomposites exhibited mixed intercalated and
exfoliated behavior than the neat one. The percentage of exfo-
liation is more in the case of 1% and 3 wt% loaded system than
5 wt% loaded one. This is indicative of effective dispersion of F-
nAl within epoxy, which could be achieved only at low weight
percentages. Surface morphological results from SEM, TEM and
AFM show that the 3 wt% loaded F-nAl TGBAPSB nano-
composites exhibit mono dispersity while 5 wt% loaded F-nAl
TGBAPSB nanocomposites exhibit aggregation. It was also
observed that upon comparing the tensile, exural and impact
properties of neat and F-nAl reinforced composite systems, a
benecial increase in mechanical properties for the reinforced
nanocomposite systems was observed. The nanoreinforcement
(F-nAl) produced a signicant improvement on the thermal
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constant indicating the best insulation properties. Thus the
TGBAPSB epoxy resin reinforced with optimized F-nAl loading
possess better mechanical, thermal and thermo mechanical
insulation characteristic than those of conventional and di-
functional epoxy materials. Hence the material developed in the
present work could be explored for a possible high performance
and industrial applications that require improved durability.
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Acknowledgements
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Instrumentation facility provided under FIST-DST and DRS-
UGC to Department of chemistry, Anna University, Chennai is
grate fully acknowledged.
27 B. Akbari and R. Bagheri, Eur. Polym. J., 2007, 43, 782.
28 S. Zainuddin, M. V. Hosur, Y. Zhou, A. T. Narteh, A. Kumar
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40140 | RSC Adv., 2014, 4, 40132–40140
This journal is © The Royal Society of Chemistry 2014