Radiation cured epoxy acrylate composites based on graphene, graphite oxide and functionalized graphite oxide with enhanced properties

Article abstract of DOI:10.1166/jnn.2012.5185

Epoxy acrylate (EA) composites containing graphite oxide (GO), graphene and nitrogen-double bond functionalized graphite oxide (FGO) were fabricated using UV-radiation and electron beam radiation via in-situ polymerization. Graphene and FGO were homogenously dispersed in EA matrix and enhanced properties, including thermal stability, flame retardancy, electrical conductivity and reduced deleterious gas releasing in thermo decomposition were obtained. Microscale combustion colorimeter results illustrated improved flame retardancy; EA/FGO composites achieved a 29.7% reduction in total heat release (THR) when containing only 0.1% FGO and a 38.6% reduction in peak-heat release rate (PHRR) when containing 3% FGO. The onset decomposition temperatures were delayed and the maximum decomposition values were reduced, according to thermogravimetric analysis which indicated enhanced thermal stabilities. The electrical conductivity was increased by 6 orders of magnitude (3% graphene) and the deleterious gas released during the thermo decomposition was reduced with the addition of all the graphite samples. This study represented a new approach to functionalize GO with flame retardant elements and active curable double bond to achieve better dispersion of GO into polymer matrix to obtain nanocomposites and paved a way for achieving graphene-based materials with high-performance of graphene in enhancement of flame retardancy of polymers for practical applications. Copyright

Full text of DOI:10.1166/jnn.2012.5185

Copyright © 2012 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 12, 1776–1791, 2012
Radiation Cured Epoxy Acrylate Composites Based on
Graphene, Graphite Oxide and Functionalized
Graphite Oxide with Enhanced Properties
∗
Yuqiang Guo, Chenlu Bao, Lei Song, Xiaodong Qian, Bihe Yuan, and Yuan Hu
State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
Epoxy acrylate (EA) composites containing graphite oxide (GO), graphene and nitrogen-double
bond functionalized graphite oxide (FGO) were fabricated using UV-radiation and electron beam
radiation via in-situ polymerization. Graphene and FGO were homogenously dispersed in EA matrix
Delivered by Ingenta to:
and enhanced properties, including thermal stability, flame retardancy, electrical conductivity and
University of South Australia
reduced deleterious gas releasing in thermo decomposition were obtained. Microscale combustion
colorimeter results illustrated improvedIflPam:e95re.t2ar7d.a0n.c6y3; EA/FGO composites achieved a 29.7%
reduction in total heat release (THR) when containing only 0.1% FGO and a 38.6% reduction in
Sun, 24 Jun 2012 07:41:06
peak-heat release rate (PHRR) when containing 3% FGO. The onset decomposition temperatures
were delayed and the maximum decomposition values were reduced, according to thermogravimet-
ric analysis which indicated enhanced thermal stabilities. The electrical conductivity was increased
by 6 orders of magnitude (3% graphene) and the deleterious gas released during the thermo
decomposition was reduced with the addition of all the graphite samples. This study represented a
new approach to functionalize GO with flame retardant elements and active curable double bond to
achieve better dispersion of GO into polymer matrix to obtain nanocomposites and paved a way for
achieving graphene-based materials with high-performance of graphene in enhancement of flame
retardancy of polymers for practical applications.
Keywords: Graphene, Radiation Curing, Flame Retardancy, Thermal Stability, Deleterious Gas
Release.
1
. INTRODUCTION
remedy these disadvantages, polymers are often com-
pounded with a variety of fillers such as clay, layer
As one of the most interesting materials, graphene has
triggered enormous interest due to its unique proper-
ties induced by its 2D one-atom thick carbon layer
structure. Individual graphene combines extraordinary
high aspect ratio, enormous specific surface, high val-
ues of Young’s modulus (∼1100 GPa), fracture strength
double hydroxide (LDH), expandable graphite, graphite
11–23
oxide and carbon nanotubes, etc.
Recently, graphene-
polymer composites have been a hot issue due to the
comprehensive and efficient enhancements in various prop-
erties. The incorporation of graphene usually leads to
significantly enhanced properties such as mechanical prop-
erties, electrical conductivity and gas resistance, etc.1
It is well known that the dispersion and interface are
two key factors to improve the property performance of
polymer composites based on 2-D layered materials.2
Lamentedly, graphene easily re-aggregates due to its high
surface area and the strong intrinsic van der Waals force
between the nano-sheets, which counteracts its disper-
sion in polymer matrix. Thus, functionalized graphene
(oxide) with functional groups on graphene (oxide) sur-
face which may improve the dispersion and interaction
(
∼125 GPa), elastic modulus (∼0.25 TPa), thermal con-
0ꢁ24–26
−1 −1
2
ductivity (∼5000 Wm
K
V
ꢀ and mobility of charge
−1
−1 1–4
etc, which endow
carriers (∼200000 cm
s
ꢀ,
graphene with great potential applications such as pho-
tovoltaic devices, sensors, transparent electrodes and
7–28
5
–10
supercapacitors.
Polymers are widely used in various fields for their
flexibility, chemical resistance, endurance, waterproofing,
low density and low cost. However, most polymers are
flammable and the mechanical properties are far away
from perfect, which limit their industrial application. To
has been a promising strategy to obtain high performance
∗
28–33
Author to whom correspondence should be addressed.
polymer composites.
In addition, the layered structure
1
776
J. Nanosci. Nanotechnol. 2012, Vol. 12, No. 3
1533-4880/2012/12/1776/016
doi:10.1166/jnn.2012.5185

Guo et al. Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties
of graphene and its derivate slows down the diffusion of
pyrolysis products and oxygen in the thermo decompo-
sition process, acting as physical barrier to increase the
thermal stability of polymer composites, similar to that
of montmorillonite (MMT) and layered double hydroxide
2.2. Preparation of Graphite Oxide, Graphene and
Functionalized Graphite Oxide
The preparation route is shown in Scheme 1.
Graphite oxide (GO) was prepared by modified Hum-
mers’ method. Briefly, 115 mL H SO was placed in a
(
LDH), both of which have attracted considerable attention
2
4
3
4–38
four-neck flask and cooled in an ice bath, followed by
the addition of 5 g expandable graphite (EG) and 2.5 g
in the past two decades in polymer nanocomposites.
However, due to its large value of thermal conductivity,
graphene layers are not good barrier to slow down the heat
transfer, thus it has not present obvious effect to improve
the flame retardancy in polymer composites.
Herein, in order to efficiently improve the dispersion
of graphene nano-sheets in polymeric matrix and enhance
the flame retardancy of polymer composites, flame retar-
dant elements and active double bond which can be cured
with epoxy acrylate were introduced. Chemical reduction
of graphite oxide (GO) has been the most convenient
way to obtain graphene, which also offers chemical active
ꢀ
NaNO . The mixture was stirred for 15 min below 5 C,
3
then 37.5 g KMnO was slowly added and the temperature
4
ꢀ
ꢀ
was controlled between 16 C and 20 C. After 30 min
ꢀ
ꢀ
stirring below 10 C, the mixture was heated to 35 C
to react for 60 min. Then 230 mL deionized water was
added dropwise into the mixture and the temperature was
ꢀ
controlled at 96–98 C. After 30 min reaction, the viscous
mud was diluted by 1000 mL water and suitable amount
of 30% H O was added to reduce the unreacted KMnO
2
2
4
until the slurry turned golden yellow. The suspension was
centrifuged, washed with dilute hydrochloric acid and hot
points, making chemical functionalization realDizeablilev.eSrteardt-by Ingenta to:
ing from GO, graphene and functionalizeUd gnriavpehirtseitoyxidoef South Australia
water until the pH value reached ∼7, and finally wet GO
was obtained.
(
FGO) were prepared and incorporated into epoxy acrylic.
IP : 95.27.0.63
In a typical procedure to prepare graphene, wet GO
Epoxy acrylic (EA) with high adhesion and high strength
is a UV curable polymer widely used in industry, whereas
the flammable defect restricts some applications, thus
flame retardant systems to reduce the fire hazards are
needed to be introduced. The blending was cured with a
radiation curing method, which can instantaneously con-
vert low-viscosity oligomer into a polymerized and cross-
linked polymer network with reduced solvent emission.39
The obtained composites, particularly EA/graphene and
EA/FGO composites, present improved electrical conduc-
tivity, enhanced flame retardancy and reduced gas releas-
ing, which may improve the industrial application of EA
and graphene.
Sun, 24 Jun 2012 07:41:06
was dispersed in deionized water with ultrasonication until
no visible particle was observed. Hydrazine hydrate (mass
ratio of GO: hydrazine about 10:7) was added and the
ꢀ
mixture was heated in an oil bath at 90 C under a reflux
condenser for 8 h. Graphene gradually precipitated out as
black particles which was centrifuged and washed with
acetone to get graphene acetone dispersion.
To prepare FGO, isophorone diisocyanate (IPDI,
0
.02 mol, 4.448 g), 4-methoxyphenol (0.068 g, inhibitor)
and dibutyltin dilaurate DBTD (6.8 mg, catalyst) were
poured into a three-necked flask equipped with a nitro-
gen inlet, a mechanical stirrer, a reflux condenser and a
dropping funnel; the flask was filled with nitrogen and
ꢀ
put into an oil-bath at 40 C, and HEA (2.23 g, 0.2 mol)
2. EXPERIMENTAL DETAILS
was slowly dropped in. The reaction lasted 12 hours at
ꢀ
5
0 C and was maintained for 12 h to obtain IPEA. After
2.1. Materials
that, 4-methoxyphenol (0.068 g) and DBTD (6.8 mg) were
added into the as-obtained blending with stirring; 0.5 g
GO (in 20 mL acetone) was then added and the tempera-
Expandable graphite (EG, mesh 325, purity >99%)
was supplied by Qingdao Tianhe Graphite Co., Ltd
ꢀ
(
China). Potassium permanganate (KMnO ꢀ, hydrochloric
ture was kept at 60 C. After 12 hours mechenical stirring,
4
acid (HCl), sodium nitrate (NaNO ), ethanol (C H OH),
the mixture was filtered and washed with deionzed water
and chloroform to remove triethylamine hydrochloride and
impurities, and FGO was finally obtained.
3
2
5
hydrazine hydrate (85%), hydrogen peroxide (H O ꢀ
2
2
and dibutyltin dilaurate (DBTD) were purchased from
Sinopharm Chemical Reagent Co., Ltd. (China); bisphe-
nol A epoxy acrylate, with a unsaturation concentration
2
.3. Preparation of Epoxy Acrylic Resin Based
Nanocomposites
−1
−1
of 3.73 mmol g and a molar mass of 536 g mol ,
was supplied by Tianjin Tianjiao Co. (China); isophorone
diisocyanate (IPDI) was purchased from the First Reagent
Co. of Shanghai (China) and it was distilled before use;
The EA/GO nanocomposites were prepared as follows:
first, GO was dispersed in acetone with ultrasonication to
obtain well dispersed suspension which was then added
2-hydroxylethyl acrylate (HEA) was supplied by Dong-
fang Chemical Co (China) and it was distilled before
use. 2-Hydroxy-2-methyl-1-phenyl-1-propanone (Darocur
to the EA oligomer with stirring for 0.5 hour. The homo-
ꢀ
geneous solution was put in a vacuum oven at 50
C
1
173, photoinitiator) was kindly supplied by Ciba Spe-
overnight to remove the solvent. Second, 3% Darocur
1173 (photoinitiator) were dropped into the mixture with
cialty Chemicals (Singapore).
J. Nanosci. Nanotechnol. 12, 1776–1791, 2012
1777

Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties Guo et al.
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Scheme 1. Preparation route of functionalized GO.
1
778
J. Nanosci. Nanotechnol. 12, 1776–1791, 2012

Guo et al. Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties
stirring to obtain homogenous blending which was then
poured into a stainless steel mold, followed by pre-curing
spectrophotometer (Nicolet Instrument Company, USA).
About 5.0 mg of the sample was put in an alumina cru-
−1
ꢀ
using UV irradiation equipment (80 W cm , Lantian
Co., China). Third, the molded samples were irradiated
using an electron beam accelerator (RDI-Dynamitron,
DPC-2000 Control System, Dasheng Co., China) under
forced air cooling with irradiation doses (60 kGy). Finally,
the EA/GO composites were obtained. EA/graphene and
EA/FGO composites were prepared with the same process.
cible and heated from 30 to 650 C at a heating rate of
ꢀ
20 C/min (nitrogen atmosphere, flow rate of 45 ml/min).
Combustion testing was performed using GOVMARK
MCC-2 Micro Combustion Colorimeter (MCC, USA). The
2
incident heat flux was 45 kW/m and about 5 mg of each
ꢀ
ꢀ
sample was heated to 650 C at a heating rate of 1 C/s
3
and in a stream of nitrogen flowing at 80 cm /min; each
test was repeated twice.
EA composites were scanned by differential scanning
calorimetry (DSC) at 50 C/min ramping to investigate
the influence of various forms of graphite on the glass
2
.4. Characterization
ꢀ
X-ray diffraction (XRD) pattern was performed on the
1
mm thick films with a Japan Rigaku D/Max-Ra rotat-
transition temperature (T ꢀ.
g
ing anode X-ray diffractometer equipped with a Cu Kꢂ
tube and Ni filter (ꢃ = 0ꢄ1542 nm). The scanning rate was
ꢀ
ꢀ
3. RESULTS AND DISCUSSION
4
/min and the range was 3–65 .
Fourier transform infrared (FTIR) spectra were obtained
3
.1. Structural Characterization of EG, GO,
using Nicolet 6700 FTIR (Nicolet Instrument Company,
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Graphene and FGO
−1
USA) between 500 and 4000 cm . Samples were shaved
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to powder and mixed with KBr powders and pressed into
3.1.1. XRD
IP : 95.27.0.63
tablets before characterization.
Sun, 24 Jun 2012 07:41:06
Figure 1 shows the XRD patterns of EG, GO, graphene
and FGO. The pristine expandable graphite exhibits a
X-ray photoelectron spectroscopy (XPS) was obtained
using a VG ESCALB MK-II electron spectrometer. The
excitation source was an Al Kꢂ line at 1486.6 eV.
Atomic force microscopy (AFM) observation was per-
formed by DI Multimode V scanning probe microscope.
The samples were dispersed in water and dip-coated onto
freshly cleaved mica surfaces before the test.
ꢀ
strong (002) diffraction peak at 2ꢅ = 26ꢄ5 , corresponding
to an interlayer distance of 0.34 nm. In the pattern of GO,
ꢀ
the (002) peak increases to 10.31 , demonstrating the inter-
layer spacing expanded to 0.69 nm , which is in agreement
with previous results.40 After reduction by hydrazine, the
resulting graphene sheets present no obvious peaks, indi-
cating the exfoliation of GO sheets during the reduction
process to form individual graphene nano-sheets as con-
firmed in the AFM section. The FGO has similar pattern as
graphene, demonstrating long range disorder, and it may
be caused by the introducing of IPEA which chemically
bonds with graphite oxide during the modification process
and extends the d-spacing to form individual sheets.
Measurements of volume resistivity and surface resis-
tivity of the samples were investigated with ZC36 high
resistance meter (Cany Precision Instruments Co., LTD.,
3
China). Specimen with the size of 10 × 10 × 1 mm was
applied as the test sample.
Thermogravimetric analysis (TGA) were carried out on
a TGA Q5000IR (TA Instruments, USA) thermo-analyzer
ꢀ
ꢀ
instrument from 30 to 650 C (700 C) at a heating rate of
ꢀ
2
0 C/min under air flow. Samples of about 5.0 mg were
measured in an alumina crucible. Two parallel runs were
performed in the case of each sample.
Transmission electron microscopy (TEM) images were
obtained on a JEOL JEM-100SX microscope with an
acceleration voltage of 100 kV. TEM specimens of GO,
graphene and FGO were washed with ethanol and col-
lected on a 200 mesh copper grids. The EA nanocom-
posites were performed with ultrathin sections microtomed
using an Ultratome (Model MT-6000, Du Pont Company,
USA) equipped with a diamond knife.
The morphologies of the surface of fracture from the
composites sputtercoated with a gold layer in advance
were investigated by a scanning electron microscopy
(
SEM) AMRAY1000B (Beijing R&D center of the Chi-
nese academy of sciences, China).
Thermogravimetric analysis/infrared
TG-IR) was carried out using a TGA Q5000 IR thermo-
spectrometry
(
Fig. 1. XRD curves of the pristine expandable graphite, graphite oxide,
gravimetric analyzer interfaced to the Nicolet 6700 FTIR
graphene and functionalized graphite oxide.
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Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties Guo et al.
.1.2. FTIR
3
The FTIR spectra of samples got from the reaction ves-
sel before and after the reaction of IPEA with GO were
shown in Figure 2 to trace the functionalization process.
−1
The peak at 2267 cm corresponding to N
tion from IPEA gradually disappears, indicating the reac-
tion of N O with –OH and –COOH from GO.
C
O vibra-
C
Figure 3 shows the IR spectra of pristine EG, GO,
graphene and FGO. The small peaks on EG pattern are
caused by the intercalated acid and oxidant. The GO pat-
tern shows characteristic peaks which is in good agree-
4
1–42
ment with earlier work.
all the oxygen containing groups become very weak and
After the hydrazine reduction,
−1
a new peak around 1560 cm attributed to the stretch-
ing vibration of C C from an aromatic group appears.
In FGO, some new peaks appear: the peak at 2964 cm
corresponds to –CH –, the peak at 1535 cm is attributed
to O C–NH, a small peak at 1635 cm is assigned to
C, and two peaks at 1235 cm and 1192 cm can be
ascribed to –COO–. All of these peaks provide evidence
for the successful grafting of IPEA onto graphene sheets.
−1
Fig. 3. The FTIR spectra of graphite oxide, reduced graphite oxide and
functionalized graphite oxide.
−1
2
−1
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−1
−1
C
caused by the formation of O–C O bond during the func-
tionalized process of GO. N1s envelope region was used to
confirm the incorporation of nitrogen as shown in Figure 5.
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The faintness signal of nitrogen of GO is due to the NO2
403 eV) and NO (401 eV) groups left during the oxida-
(
3
3.1.3. XPS
tion of GO. Nitrogenated carbon signals in graphene can
be attributed to partial reduction of carbonyl functionalities
The high-resolution narrow scans of the C1s and N1s enve-
lope region of GO, graphene and FGO with the prominent
components are marked in Figures 4 and 5. In Figures 4(a)
and (b), three types of carbon can be observed: C–C, C–O
and O–C O. The reduction process results in a remark-
able decrease of O/C ratio and the peak corresponding to
C–C (284.8 eV) becomes dominant in graphene, which
confirms successful reduction of GO. In Figure 4(c), a new
peak of C–N (284.8 eV) arises, confirming the successful
bonding of IPDI and HEA onto the GO sheets, and the
increment of the relative content of O–C O (289.2 eV) is
into hydrazone groups.4
4–45
As a conclusion, functional-
ized process of FGO results in a C–N peak (399.8 eV),
indicating the successful bonding of IPEA onto the GO
sheets.
4
3
3.1.4. AFM
The AFM observations of GO, graphene and FGO with
the height profile taken along the lines inside were shown
in Figure 6. The cross-sectional view of the typical AFM
image of the exfoliated GO sheet indicated lateral dimen-
sions of hundreds of nanometers and average height of
0
.7∼0.8 nm, similar to the interlayer distance of GO
(
0.69 nm) measured by XRD. For single graphene sheets,
height profiles show steps from the mica to graphene sheet
of 0.7 nm for the given cross-section (Fig. 6(b)). Compared
to theoretical values for graphene, there is discrepancy
of 0.3∼0.4 nm in thickness demonstrating the presence
of some residual oxygen groups on the sheets which is
in agreement with other reports.46 The apparent heights
of FGO (Fig. 6(c)) sheets observed were around 1.3 nm,
larger than that of the pristine GO, which may be caused
by the modifier chemically bonding to the FGO sheets.
3
.1.5. Thermal Decomposition Behavior
The thermal decomposition behavior of GO, graphene and
FGO were analyzed in air and the results are shown in
Figure 7. Graphite oxide is not thermally stable, and its
decomposition process can be divided into two stages: the
Fig. 2. The FTIR spectra of IPEA before and after the reaction with
GO.
1
780
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Guo et al. Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties
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Fig. 5. High-resolution XPS narrow scans of the N 1s region for GO
(
a) graphene ( b) and FGO (c).
combustion of the carbon framework48 and the residual
ꢀ
char at 650 C is 13%. The thermal stability of graphene is
greatly improved due to the decrease in defect density dur-
ing the reduction process. As shown in Figure 7, graphene
ꢀ
presents no significant mass loss detected until 500 C, and
ꢀ
the char residue at 650 C is increased from 13% of GO
ꢀ
to 24%. FGO is more stable than GO below 350 C with
a reduced char residue of 0.8%. The unstable behavior at
high temperature may be caused by the functional groups
with ester bonds and urethane links.
3
.2. Electrical Microscopy Characterization of EA
Composites
Fig. 4. High-resolution XPS narrow scans of the C 1s region for GO
a) graphene (b) and FGO(c).
Via electrical microscopy, one can directly observe the
(
micro-structure and dispersion of nano-fillers in polymeric
ꢀ
11ꢁ27ꢁ49
first stage, between 200–270 C, is caused by the decom-
position of oxygen containing groups such as hydroxyl,
matrix.
From SEM images (Fig. 8), it is clear that
the GO, graphene and FGO sheets were dispersed uni-
formly into the substrate and they appeared flattened with-
out large bundles. However, the EA composites have rough
carboxyl on the graphite sheets to give birth to CO, CO
and steam; the second stage, 440∼550 C, is due to the
2
4
7
ꢀ
J. Nanosci. Nanotechnol. 12, 1776–1791, 2012
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Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties Guo et al.
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Fig. 6. AFM images of GO nanosheets dispersed in water and graphene dispersed in THF.
1
782
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Guo et al. Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties
Fig. 7. TG and DTG curves of GO, graphene and FGO in air atmosphere.
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Fig. 8. SEM micrograph showing the morphology of fracture surface of Graphite fillers in EA composites with GO (graphene or FGO) content of
1
wt%. (The scale bar is 10 ꢆm).
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Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties Guo et al.
cross-sections, indicating that nano-fillers have already
been embedded in EA matrix with good dispersion.
the interaction between graphene nano-sheets. As for the
EA/FGO composites, no big bundles were observed and
the dispersion was uniform throughout the EA matrix with
intercalated-exfoliated structure, which can be attributed
to the enhancement of interactions between FGO nano-
sheets and EA matrix due to the crosslink of EA matrix
and active double bond in FGO. Thus the incorporation of
active double bond is effective to disperse graphene/GO
sheets in polymeric matrix.
The inner structures of EA composites with 1% addi-
tion amount of graphite fillers were examined by TEM
technique as shown in Figure 9. For the EA/GO com-
posites, the dispersion of GO is not completely uniform
with some particle settlement, which is in analogy to the
fact that the oxygen-containing groups such as carboxyl
and hydroxyl groups form strong interactions including
hydrogen bond and vander Waals force interaction between
GO sheets, hindering the dispersion of GO in polymeric
matrix. For EA/graphene composites, no particle settle-
ment and aggregates were observed and isolated graphene
sheets were homogeneously dispersed in the polymer
matrix; one can observe single or few layer graphene
nano-sheets with thickness less than several nanometers,
indicating good compatibility of graphene in EA compos-
ites due to the elimination of polar groups which weakens
3.3. Electrical Properties
The volume resistivity (ꢇ ꢀ and surface resistivity (ꢇ ꢀ of
v
s
EA composites were summarized and plotted in Figure 10.
15
Pure EA has a volume resistivity of 6ꢄ2·10 ꢈ·cm and a
15
surface resistivity of 2ꢄ3·10 ꢈ/cm. With the increase of
graphite fillers addition amounts, the resistance decreases,
especially in EA/graphene composites. The volume resis-
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tivity is decreased approximately one order of magni-
tude when containing 3% GO, two orders of magnitude
when containing 3% FGO and six orders of magnitude
when containing 3% graphene, and the surface conductiv-
ity shows the similar trend.
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Fig. 9. TEM micrograph showing the dispersion of graphite fillers in
EA composites with (graphene or FGO) content of 1 wt%. (The scale
bar is 0.5 ꢆm for EA/1 wt% GO composite and 200 nm for EA/1 wt%
Graphene and EA/1 wt% FGO).
Fig. 10. The volume resistivity (ꢇ ꢀ and surface resistivity (ꢇ ꢀ of EA
composites.
v
s
1
784
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Guo et al. Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties
The high aspect ratio, large specific surface area of the
graphene sheets may provide extra charge carriers linking
the conductive channel of the EA matrix, thus increase
the conductivity. For GO and FGO composites, there are
many oxygen containing groups bonding at the edges caus-
ing defect which limits the increment in conductivity. As
edges enhancing the interaction between the FGO sheets
and the EA matrix.
3
.4. Thermal Stability and Flame-Retardant
Properties of EA and EA/G Composites
2
for graphene, the restoration of sp C–C bonds resulted
3
.4.1. TGA
in significant improvements in electrical conductivity of
EA/graphene composites. The slightly higher conductivity
of EA/FGO composites compared to EA/GO composites
at high content may be due to the double bonds at the FGO
The degradation process of EA and EA composites in
air atmosphere are investigated by TGA as shown in
Figure 11. The thermal degradation process of EA and EA
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Fig. 11. TG and DTG curves of EA composites in air atmosphere.
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Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties Guo et al.
Table I. TG data of EA composites in air.
Char residue at
ꢀ
ꢀ
ꢀ
ꢀ
700 C
Sample ID.
T-5% ( C) Tmax1 ( C) Tmax2 ( C)
EA
310
277
303
289
329
309
309
280
305
280
419
426
427
430
425
428
423
418
417
414
569
590
588
585
585
587
590
583
571
564
0
EA/0.5% GO
EA/1% GO
EA/3% GO
EA/0.5% Graphene
EA/1% Graphene
EA/3% Graphene
EA/0.5% FGO
EA/1% FGO
EA/3% FGO
1.0%
1.6%
2.0%
1.6%
2.0%
1.1%
1.4%
2.4%
1.8%
composites have two stages in the temperature ranges of
ꢀ ꢀ
50–450 C and 550–650 C, and the corresponding T
max1
3
and Tmax2 obtained from the DTG curves as well as the
onset temperature marked as T5%, and the char residue at
ꢀ
7
00 C are listed in Table I. The thermal stability of EA
is influenced a lot by the presence of graphiDte efillilevres.reTdheby Ingenta to:
onset degradation temperatures of EA/GUOnainvderEsAit/yFGoOf South Australia
composites decrease due to the unstable oxygen-conItPain:in9g5.27.0.63
groups, while the EA/graphene composites decompose
Sun, 24 Jun 2012 07:41:06
later for the elimination of oxygen containing groups on
ꢀ
graphene sheets. The Tmax1 and Tmax2 increase by 10–20 C
and the char residue increases a little in EA/GO and
EA/graphene samples, indicating improved thermal sta-
bilities. Tmax1 of EA/FGO composites shows no obvious
change, and Tmax2 increases when containing 0.5% and 1%
FGO but further decreases with 3% addition. Moreover,
the DTG peaks are decreased compared to EA. The addi-
tion of graphite fillers can improve the thermal stability
of EA composites, which can be attributed to the layer
barrier effect and the absorption of free-radicals generated
during polymer decomposition by the carbon surface. The
layered structure of graphite fillers can act as a barrier pre-
venting the transfer of combustion gases to the flame zone
5
0–52
and energy feedback to increase the thermal stability.
3.4.2. DSC
Figure 12 shows the DSC results. T of the EA composites
g
shifts to lower temperature with the increase amount of
ꢀ
ꢀ
GO (15.6 C, 3% GO), graphene (17.3 C, 3% graphene)
ꢀ
and FGO (21.4 C, 3% FGO), indicating that the graphite
layers can act as a plasticizer increasing the flexibility of
chain segments, thus improve the mobility of the EA chain
segments.
3.4.3. MCC
Fig. 12. DSC curves of EA composites showing the Tg results in N2
atmosphere.
MCC is a new, direct and effective technique to investi-
gate the combustion and heat release behaviors by directly
measuring the released heat when samples are burning.53
HRR (heat release rate) expressing the intensity of a fire is
an important parameter to predict the combustion behavior
of a material in a real fire.
The flammability properties of the EA composites are
analyzed by MCC under N and the results are shown in
Figure 13, with the HRR, THR and Tmax data summarized
in Table II. It is found that the total heat released (THR)
2
1
786
J. Nanosci. Nanotechnol. 12, 1776–1791, 2012

Guo et al. Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties
Table II. MCC data of EA composites in N2.
ꢀ
Sample ID.
PHRR (w/g)
THR (kJ/g)
Tmax ( C)
EA
331.4
243.7
234.1
205.3
253.2
241.0
228.6
235.4
227.4
210.3
21.2
21.1
20.0
17.7
16.4
16.2
14.7
14.6
15.0
15.5
440
438
435
427
436
423
424
427
417
414
EA/0.5% GO
EA/1% GO
EA/3% GO
EA/0.5% Graphene
EA/1% Graphene
EA/3% Graphene
EA/0.5% FGO
EA/1% FGO
EA/3% FGO
and the reduction is 38.6%, 32.5% and 38.6% respectively
for EA/3% GO, EA/3% graphene and EA/3% FGO. In
addition, the temperature at maximum pyrolysis rate (Tmax
ꢀ
decreases a little because of the low initial thermal stability
of the fillers. The EA/Graphene and EA/FGO composites
show better flame retardant properties than EA/GO com-
Delivered by Ingenta to:
posites, and the mechanism can be described as follows:
University of South Australia
less effectiveness of GO is cause by the oxygen-containing
IP : 95.27.0.63
groups on the GO sheet and the worse dispersion in the
Sun, 24 Jun 2012 07:41:06
EA matrix; the elimination of oxygen-containing groups
and the improved dispersion of graphene lead to increased
flame retardancy for EA/graphene composites; the flame
retardant element-nitrogen chemically bonded on the FGO
sheet enhanced the flame retardant effect and improved its
dispersion. THR and PHRR are apparently reduced in the
presence of the graphite fillers, implying that the incorpo-
ration of GO, graphene and FGO in EA can improve the
flame retardancy of EA, and the flame retardant effect of
both graphene and FGO is comparatively better than that
of GO.
3
.4.4. TG-FTIR Analysis of EA and EA-G Composites
The TG–IR technique is used to characterize the gaseous
products formed during the thermal degradation pro-
cess, which is helpful to analyze the thermal degrada-
tion mechanism.54 The 3D TG-FTIR spectra of the gases
formed in the thermal degradation of EA and EA com-
posites per milligram are shown in Figure 14. EA and EA
composites mainly evolve between 20 min and 30 min,
generating a series of sharp peaks in the 3D spectra. The
evolved gas analysis for EA, EA/1% GO, EA/1% graphene
and EA/1% FGO at maximum decomposition (shown in
Fig. 15) exhibited characteristic bands of H O and/or
phenol (3738 cm ꢀ, CO2 (2362 cm ꢀ, hydrocarbons
2
Fig. 13. HRR curves of EA/G composites from MCC test in N2
atmosphere.
−1
−1
−1
(
–CH and –CH ꢀ groups (2970 cm ꢀ, compounds con-
3
2
taining aromatic rings (676 cm ꢀ.55–56 Concluded from
Figures 14 and 15, the absorbance intensity of gases dur-
ing the degradation of EA composites decrease a lot com-
pared to neat EA especially for the EA/FGO composites,
indicating less volatile evolution.
−1
of all the EA composites decrease with increase content
of graphite fillers. Compared to pure EA, the decrement of
THR is 16.1%, 30.3% and 31.3% for EA/3% GO, EA/3%
graphene and EA/3% FGO, respectively, indicating that
graphene and FGO perform better than GO. Meanwhile,
the Peak-HRR (PHRR) decreases as the additives increase,
The absorbance of pyrolysis products for EA and EA
composites versus time is revealed in Figure 16. It can
J. Nanosci. Nanotechnol. 12, 1776–1791, 2012
1787

Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties Guo et al.
Delivered by Ingenta to:
University of South Australia
IP : 95.27.0.63
Sun, 24 Jun 2012 07:41:06
Fig. 14. 3D TG-FTIR spectrum of gas phase in the thermal degradation of EA composites.
Fig. 15. FTIR spectrum of pyrolysis products for EA, EA/1% GO, EA/1% Graphene and EA1% FGO at the maximum decomposition rate.
1
788
J. Nanosci. Nanotechnol. 12, 1776–1791, 2012

Guo et al. Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties
be seen that the pyrolysis products for all the composites
begin to release at about 20 min, and the EA/1%GO com-
posite pyrolyzes a little earlier whereas EA/1%graphene
and EA/1%FGO have the delayed phenomena. These dif-
ferences suggest that composites containing GO degrade
earlier than EA itself. In addition, the absorbance intensity
of pyrolysis products for EA composites is lower than that
for EA, especially the EA/1%FGO composite. The results
of the pyrolysis products release is in good accordance to
the MCC and TG results, and it can be interpreted that GO,
graphene and FGO can reduce the release of combustible
gases and the weight loss.
slowing down the heat released and hindering the transfer
of combustion gases and energy feedback, which is sim-
ilar to the performance of MMT and LDH.36 Secondly,
the various graphite fillers increase the melt viscosity and
hinder the thermal movement of polymer chains, similar
to the effect of CNT reported elsewhere.59 In addition, the
enormous specific surface of the sheets which is about
2600 m g reported elsewhere may act as a radical
scavenger to terminate the active radicals generated dur-
ing the thermal degradation process, which needs further
investigation.
However, differences in the thermal degradation and
flame retardancy performance should be listed. GO
degrades earlier than pure EA due to the oxygen-
containing groups, thus the onset temperature from the
TGA test and the time of maximum decomposition from
the TG-IR test of EA/GO composites decrease and that is
why the THR of the MCC test is relatively higher com-
pared to EA/graphene and EA/FGO composites. PHRR is
2
−1
60
3.4.5. Flame Retardancy and Thermal Degradation
Mechanism
Polymer nanocomposites usually present improved flame
5
7ꢁ58
retardancy and thermal stability.
TGA, TG-IR and
MCC studies of the composites demonstrate that the
graphite samples can reduce the release of combustible
Delivered by Ingenta to:
a little lower which can be ascribed to the decomposition
in advance thus reduce the crest value of HRR. Compared
to GO, the elimination of the oxygen containing groups
on graphene sheets increases the onset degradation tem-
perature and largely reduces the THR values. The max-
imum decomposition rate of EA/graphene composites is
University of South Australia
gases and heat. There are three possible mechanisms
responsible for the improvement in flame retardancy and
IP : 95.27.0.63
Sun, 24 Jun 2012 07:41:06
thermal degradation as can be concluded as follows:
Firstly, as a layered nano-filler, the graphite materials
dispersed in the matrix can act as a barrier effectively
Fig. 16. Absorbance of pyrolysis products for EP and EP3 versus time: (a) hydrocarbons; (b) CO ; (c) carboxylic acid and (d) aromatic compounds.
2
J. Nanosci. Nanotechnol. 12, 1776–1791, 2012
1789

Radiation Cured EA Composites Based on Graphene, GO and Functionalized Graphite Oxide with Enhanced Properties Guo et al.
delayed (TG-IR section). Attributed to the chemical bond
between the FGO and EA matrix, better performance is
anticipated. The lowest value of both the PHRR and THR
of EA/FGO are obtained, and the maximum decomposi-
tion rate is reduced to a large extend (Fig. 15(d)), with the
fewest pyrolysis products compared to other composites.
4. S. V. Morozov, K. S. Novoselov, M. I. Katsnelson, F. Schedin,
D. C. Elias, J. A. Jaszczak, and A. K. Geim, Phys. Rev. Lett. 100
(
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. Y. W. Chang, S. W. Yu, C. H. Liu, and R. C. C. Tsiang,
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4. CONCLUSIONS
In this research, GO, graphene and FGO were prepared
and used as nano-fillers incorporated into epoxy acrylic
resin cured by in-situ UV-radiation and electron beam radi-
ation to prepare series of composites containing 0.5%,
22, 1392 (2010).
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1
%, 3% of additives to investigate their electrical, ther-
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1
v
s
composite are reduced for six orders of magnitude. The
TGA results indicate that the graphite samples can delay
12. H. Miyagawa, M. Misra, and A. K. Mohanty, J. Nanosci. Nanotech-
nol. 5, 1593 (2005).
Delivered by Ingenta to:
13. K. A. S. Fernando, Y. Lin, B. Zhou, M. Grah, R. Joseph, L. F. Allard,
the degradation process and decrease the DTG peak val-
University of South Australia
and Y. P. Sun, J. Nanosci. Nanotechnol. 5, 1050 (2005).
Haggenmueller, W. Zhou, J. E. Fischer, and K. I. Winey,
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IP : 95.27
1
.
4
0.63
.
R
.
strate a considerable reduction of HRR and THR with
Sun, 24 Jun 2012 07:41:06
small amount of graphite fillers, indicating flame retardant
15. S. S. Ray, K. Okamoto, P. Maiti, and M. Okamoto, J. Nanosci. Nano-
technol. 2, 171 (2002).
effect of graphite sample in EA composites. The TG-IR
reveals that graphite sample can reduce the gas released,
especially FGO, which maybe due to the radical trapping
effect and layered effect hindering the transfer of com-
bustion gases to the flame zone and energy feedback and
thus enhance the flame retardancy and promote the char
formation. From this study, we confirm that the graphite
samples we prepared can improve the electrical conduc-
tivity, thermal stability, flame retardancy and reduce the
deleterious gas releasing in thermo decomposition of the
epoxy acrylic composites, especially graphene and func-
tionalized graphite oxide. Our work provides a way to
modified GO with double bond and flame retardant ele-
ments to enhance the dispersion and flame retardancy of
GO in polymer matrix, and more work it needed to inves-
tigate the flame retardant performance and mechanism of
graphene in other polymers.
1
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2
Acknowledgments: This work was financially sup-
ported by the joint fund of NSFC and Civil Aviation
Administration of China (No. 61079015) and the joint fund
of National Natural Science Foundation of China (NSFC)
and Guangdong Province (No. U1074001).
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1791