Functionalized graphite nanoplatelets/epoxy resin nanocomposites with high thermal conductivity

Abstract

Graphite nanoplatelets (GNPs) are performed to fabricate GNPs/bisphenol-A epoxy resin (GNPs/E-51) nanocomposites with high thermal conductivity via casting method. And the "two-step" method of methanesulfonic acid/γ-glycidoxypropyltrimethoxysilane (MSA/KH-560) is introduced to functionalize the surface of GNPs (fGNPs). The KH-560 molecules have been successfully grafted onto the surface of GNPs. The thermal conductivities of the fGNPs/E-51 nanocomposites are increased with the increasing addition of fGNPs, and the corresponding thermally conductive coefficient of the fGNPs/E-51 nanocomposites is improved to 1.698 W/mK with 30 wt% fGNPs, 8 times higher than that of original E-51 matrix. The flexural strength and impact strength of the fGNPs/E-51 nanocomposites are optimal with 0.5 wt% fGNPs. The thermal stabilities of the fGNPs/E-51 nanocomposites are also increased with the increasing addition of fGNPs. For a given GNPs loading, the surface functionalization of GNPs by MSA/KH-560 exhibits a positive effect on the thermal conductivities and mechanical properties of the nanocomposites.

Full text

Functionalized graphite nanoplatelets/epoxy resin nanocomposites
with high thermal conductivity
Junwei Gu
⇑
, Xutong Yang, Zhaoyuan Lv, Nan Li, Chaobo Liang, Qiuyu Zhang
⇑
Key Laboratory of Space Applied Physics and Chemistry, Ministry of Education, Department of Applied Chemistry, School of Science, Northwestern Polytechnical University,
Xi’an, Shaan Xi 710072, PR China
article info
Article history:
Received 7 April 2015
Received in revised form 3 July 2015
Accepted 25 August 2015
Available online 7 September 2015
Keywords:
Thermally conductive nanocomposites
Graphite nanoplatelets (GNPs)
Bisphenol-A epoxy resin (E-51)
Surface functionalization
abstract
Graphite nanoplatelets (GNPs) are performed to fabricate GNPs/bisphenol-A epoxy resin (GNPs/E-51)
nanocomposites with high thermal conductivity via casting method. And the ‘‘two-step” method of
methanesulfonic acid/
c
-glycidoxypropyltrimethoxysilane (MSA/KH-560) is introduced to functionalize
the surface of GNPs (fGNPs). The KH-560 molecules have been successfully grafted onto the surface of
GNPs. The thermal conductivities of the fGNPs/E-51 nanocomposites are increased with the increasing
addition of fGNPs, and the corresponding thermally conductive coefficient of the fGNPs/E-51 nanocom-
posites is improved to 1.698 W/mK with 30 wt% fGNPs, 8 times higher than that of original E-51 matrix.
The flexural strength and impact strength of the fGNPs/E-51 nanocomposites are optimal with 0.5 wt%
fGNPs. The thermal stabilities of the fGNPs/E-51 nanocomposites are also increased with the increasing
addition of fGNPs. For a given GNPs loading, the surface functionalization of GNPs by MSA/KH-560 exhi-
bits a positive effect on the thermal conductivities and mechanical properties of the nanocomposites.
Ó2015 Elsevier Ltd. All rights reserved.
1. Introduction
Thermal interface materials (TIMs) play an important role in the
electronic components area due to the continued miniaturization
and light weight [1–3]. Polymers have gained wider applications
in different branches of industry because of their light weight,
low cost and excellent chemical resistance, etc. [4–7]. However,
the intrinsic low thermal conductivities of the polymers have lim-
ited their broader applications, especially in the fields of dissipat-
ing heat and maintaining operating temperature.
In our previous work, several thermally conductive polymeric
composites have been successfully fabricated by adding single or
hybrid thermally conductive fillers, such as silicon carbide (SiC)
[8,9], aluminum nitride (AlN) [10], boron nitride (BN) [11], gra-
phite nanoplatelets (GNPs) [12,13] and SiC whisker/SiC particle
(SiCw/SiCp) [14,15]. However, the improvement of the thermal
conductivities of the polymeric composites is often less than
expected from previous theory design. Furthermore, to fabricate
polymeric composites with highly thermal conductivity, the exces-
sive addition of thermally conductive fillers can create a significant
challenge of processing behavior and mechanical properties of the
polymers [16].
Epoxy resins possess high mechanical properties, excellent
dimensional & thermal stabilities, low cost and easy processing
[17–21]. However, the intrinsic low thermal conductivity of epoxy
resins has limited their wider application in microelectronic pack-
aging. Graphite nanoplatelets (GNPs) possess super diameter/
thickness ratio, and can contact with each other easily inner the
polymeric matrix [12,13]. Moreover, the value of thermal conduc-
tivity for GNPs is reported to be as high as 3000–5000 W/mK
[22,23], similar to that of graphene (theoretical value of 5000 W/
mK) [24–26]. However, the price of GNPs is about 65 dollars/kg,
much cheaper than that of graphene (more than 500 dollars/kg).
Therefore, it is expected that GNPs are suitable for fabricating the
epoxy resins nanocomposites with more highly thermal conductiv-
ity and a relatively lower cost.
In our present work, graphite nanoplatelets (GNPs) are intro-
duced to fabricate GNPs/bisphenol-A epoxy resin (GNPs/E-51)
nanocomposites with high thermal conductivity via casting
method. And the ‘‘two-step” method of methanesulfonic
acid/
c
-glycidoxypropyltrimethoxysilane (MSA/KH-560) is per-
formed to functionalize the surface of GNPs (fGNPs). The surface
performance of pristine GNPs and fGNPs are analyzed and charac-
terized by static precipitation, X-ray photoelectron spectroscopy
(XPS), Fourier transform infrared (FTIR) and thermogravimetric
analyzer (TGA). In addition, the mass fraction and surface function-
alization of GNPs affecting on the mechanical properties, thermal
http://dx.doi.org/10.1016/j.ijheatmasstransfer.2015.08.081
0017-9310/Ó2015 Elsevier Ltd. All rights reserved.
⇑
Corresponding authors. Tel./fax: +86 29 88431621.
E-mail addresses: gjw@nwpu.edu.cn (J. Gu), qyzhang1803@gmail.com
(Q. Zhang).
International Journal of Heat and Mass Transfer 92 (2016) 15–22
Contents lists available at ScienceDirect
International Journal of Heat and Mass Transfer
journal homepage: www.elsevier.com/locate/ijhmt

conductivities and thermal stabilities of the nanocomposites are
also investigated.
2. Experiments
2.1. Materials
Graphite nanoplatelets (GNPs), KNG-180, with diameter of
40
l
m, super diameter/thickness ratio of 250, are received from
Xiamen Knano Graphene Technology Co. Ltd. (Fujian, China);
Bisphenol-A epoxy resin (E-51), is received from Xi’an Resin Fac-
tory (Shaanxi, China); Both methyl hexahydrophthalic anhydride
(MeHHPA) and 2, 4, 6-tris (dimethylaminomethyl) phenol
(DMP-30), are purchased from Xi’an Hangang Chemical Group
Co., Ltd (Shaanxi, China); Methanesulfonic acid (MSA) is received
from Chengdu Kelong Chemical Co. Ltd. (Sichuan, China);
c
-glycidoxypropyltrimethoxysilane (KH-560) is supplied by
Nanjing Shuguang Chemical Group Co., Ltd. (Jiangsu, China); Ace-
tone, ethanol (EtOH) and tetrahydrofuran (THF) are all supplied
by Tianjin Fu Yu Fine Chemical Co., Ltd. (Tianjin, China).
2.2. Surface functionalization of GNPs (fGNPs)
GNPs are firstly immerged in EtOH and THF for 24 h at room
temperature for each step, then washed by distilled water, and
finally dried at 100 °C in a vacuum oven for 24 h; The obtained
GNPs are then immersed in 30 wt% MSA/distilled water for 36 h
at 80 °C, and then washed by 10 wt% NaOH and distilled water in
sequence; The mixtures of obtained GNPs (HO-g-GNPs) and KH-
560/EtOH/distilled water (1/50/50, wt/wt/wt) are reacted for 6 h
at 70 °C. Finally, the MSA/KH-560 functionalized GNPs (fGNPs)
are washed by EtOH and distilled water in sequence, and finally
dried at 120 °C in a vacuum oven for 24 h.
2.3. Fabrication of the nanocomposites
The mixtures of E-51 matrix, MeHHPA, DMP-30 and GNPs are
stirred uniformly firstly, degassed in a vacuum vessel to remove
air bubbles, and then poured into the preheated glass mold. Finally
the mixtures above are cured according to the following technol-
ogy: 100 °C/1 h + 120 °C/2 h + 150 °C/4 h, followed by post-curing
at 190 °C for another 3 h.
2.4. Analysis and characterization
X-ray photoelectron spectroscopy (XPS) analyses of the samples
are carried out by K-Alpha equipment (Thermo Electron Corpora-
tion, USA) to measure element components on the surface of GNPs
and fGNPs; Differential scanning calorimetry (DSC) analyses of the
samples are carried out at 10 °C/min (nitrogen atmosphere), over
the whole range of temperature (40–200 °C) by DSC1 (Mettler-
Toledo Corporation, Switzerland); Thermal gravimetric (TG) analy-
ses of the samples are carried out at 10 °C/min (argon atmosphere),
over the whole range of temperature (40–800 °C) by STA 449F3
(NETZSCH, Germany); Scanning electron microscopy (SEM) mor-
phologies of the samples are analyzed by VEGA3-LMH (TESCAN
Corporation, Czech Republic); Thermal conductive coefficients of
the samples are measured using a Hot Disk instrument (AB Corpo-
ration, Sweden) by standard method (Isotropic), which is based
upon a transient technique. The measurements are performed on
two parallel samples by putting the sensor (3.2 mm diameter)
between two slab shape samples. The sensor supplies a heat pulse
Fig. 1. Dispersion states of pristine GNPs and fGNPs in different solvents.
16 J. Gu et al. / International Journal of Heat and Mass Transfer 92 (2016) 15–22

of 0.03 W for 20 s to the sample and the associated change in tem-
perature is recorded. And the thermal conductivity of the individ-
ual samples is obtained [2]. Flexural strength of the samples is
measured by Electron Omnipotence Experiment Machine SANS-
CMT5105 (Shenzhen New Sansi Corp., China) at ambient tempera-
ture according to standard ISO178-1993, the testing speed is
2 mm/min and the corresponding dimension of specimen is
80 mm 15 mm 4 mm. Impact strength of the samples is mea-
sured by ZBC-4B impact testing machine (Shenzhen New Sansi
Corp., China) at ambient temperature according to standard ISO
179-1993, the impact speed is 2.9 m/s and the corresponding
dimension of specimen is 80 mm 10 mm 4 mm.
3. Results and discussion
3.1. Surface functionalization of GNPs
The dispersion states of pristine GNPs and fGNPs in different
solvents are shown in Fig. 1. Compared with that of pristine GNPs,
fGNPs can maintain stability in the acetone, EtOH, distilled water
and THF for more than 12 h. The reason is that surface functional-
ization of GNPs (fGNPs) leads to creation of sterical barrier of sta-
bilization, finally to provide remarkably stable suspension.
Fig. 2 shows entire XPS scanning spectra of pristine GNPs and
fGNPs, and the results calculated by sensitivity factor are listed
in Table 1. There are carbon (C) and oxygen (O) elements on the
pristine GNPs’ surface. After the surface functionalization of GNPs
(fGNPs), the content of C element is increased slightly. However,
O element has a slight decrease. Meanwhile, the silicon (Si) ele-
ment is also appeared on the fGNPs’ surface, which confirms that
KH-560 molecules have been introduced onto the GNPs’ surface.
To further analyze the component changes of fGNPs surface, the
deconvolution of C1s and Si2p peaks for the spectra of fGNPs is car-
ried out using Gaussian–Lorentzian fit, and the contents of C, Si and
other possible groups are calculated according to the square of vary
peaks, shown in Tables 2 and 3. Results show that the –C–Si– peak
is only 10.74% of C near 283.64 eV in Cls peak of fGNPs, and the cor-
responding peaks of –C–C– and
C
O
O
are about 72.69% and
16.57% of C respectively. Meantime, the devolution of the Si2p
shows that the binding energy of 43.28% of Si increases by
2.52 eV besides existing of Si near 100.74 eV. We can deduce that
the increasing binding energy of 43.28% of Si is for a chemical
bonding of KH-560 to GNPs surface to form –C–O–Si– [9].
Fig. 3 shows FTIR curves of pristine GNPs and fGNPs. Strong
peak at 3430 cm
1
can be assigned to the hydroxyl (–OH) stretch-
ing vibration peak, and the band at 1620 cm
1
is ascribed to the
absorption vibration peak of C@C bond. The band at 1070 cm
1
belongs to the absorption peak of CAO bond. After the surface
functionalization of GNPs (fGNPs), a new characteristic vibration
peak of SiAC is appeared near 650 cm
1
, and the band near
1050 cm
1
is also appeared owing to the appearance of SiAO from
KH-560 molecules. It demonstrates that the KH-560 molecules
have been introduced onto the GNPs’ surface.
TGA curves of pristine GNPs and fGNPs are presented in Fig. 4.
The weight loss of pristine GNPs at 800 °C is less than 1.0 wt%,
which is mainly ascribed to the loss of absorbed water on GNPs’
surface. After the surface functionalization of GNPs (fGNPs), the
weight of fGNPs is also less than 1.0 wt% at the beginning of the
experiment (40–275 °C), the moment is mostly due to rudimental
1200 1000 800 600 400 200 0
Pristine GNPs
fGNPs
C1s
Intensity
Binding Energy / eV
Si2p
Si2s
O1s
Fig. 2. XPS scanning spectra of pristine GNPs and fGNPs.
Table 1
Elements content on the surface of pristine GNPs and fGNPs.
Samples Content of elements/%
COSi
GNPs 86.34 13.66 –
fGNPs 87.95 9.22 2.83
Table 2
Components of C1s spectra of fGNPs.
Number of C1s sub-peaks Peak position/eV X
AT
/% Corresponding group
C1 283.64 10.74
CSi
C2 284.28 72.69
C C
C3 285.66 16.57
C
O
O
Table 3
Components of Si2p spectra of fGNPs.
Number of Si2p sub-peaks Peak position/
eV
X
AT
/% Corresponding
group
Si1 100.74 56.72
CSi
Si2 103.26 43.28
CSiO
3500 3000 2500 2000 1500 1000 500
Pristine GNPs
fGNPs
Wavenumber/cm-1
-OH
C=C
C-O
Si-C
Si-O
Fig. 3. FTIR curves of pristine GNPs and fGNPs.
J. Gu et al. / International Journal of Heat and Mass Transfer 92 (2016) 15–22 17

solvent and other volatilization vaporizing on the fGNPs’ surface.
The weight loss of the fGNPs reaches 1.4 wt% over the range of
275–425 °C, the moment can be contributed that the KH-560
molecule begins to decompose largely. And the weight loss of the
fGNPs gets to about 3.1 wt% in the later stages of the experiment
(425–800 °C), the moment KH-560 molecule chars and further
decomposes, till all organic compounds volatilizes.
3.2. Thermal conductivities of the nanocomposites
The mass fraction and surface functionalization of GNPs influ-
encing on the thermal conductivities of the nanocomposites are
shown in Fig. 5.
The thermal conductivities of the GNPs/E-51 nanocomposites
are increased with the increasing addition of GNPs. For a given
GNPs loading, the surface functionalization of GNPs by
MSA/KH-560 can further improve the thermal conductivities of
the nanocomposites. The thermally conductive coefficient of the
fGNPs/E-51 nanocomposite is greatly improved to 1.698 W/mK
with 30 wt% fGNPs, 8 times higher than that of pristine E-51 matrix
(0.201 W/mK).
With a small amount addition of GNPs, there is smaller incre-
ment for the thermal conductivities of the GNPs/E-51 nanocom-
posites, which is ascribed to hardly contacting of GNPs–GNPs.
With the increasing addition of GNPs, the corresponding thermally
conductive channels of GNPs–GNPs are easily formed (Shown in
Fig. 6 and Table 4), thus the thermal conductivities of the GNPs/
E-51 nanocomposites are obviously improved. Herein, the EDS
analysis can confirm that the white substances (in Fig. 6) on the
fracture surface of the fGNPs/E-51 nanocomposites are fGNPs,
which could provide the corresponding proof of the GNPs contacts
to some extent. For a given GNPs loading, fGNPs possess better
interfacial compatibility and lower interfacial thermal resistance
with E-51 matrix, which are in favor of the phonon transport,
finally to further increase the thermal conductivities of the
fGNPs/E-51 nanocomposites.
3.3. Mechanical properties of the nanocomposites
Fig. 7 shows the mass fraction and surface functionalization of
GNPs influencing on the mechanical properties of the
nanocomposites.
Fig. 6. Schematic diagram of thermally conductive channels formation for fGNPs/E-51 nanocomposites with 30 wt% addition of fGNPs.
0 5 10 15 20 25 30
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Thermal conductivity / (W/mK)
Mass fraction of GNPs / %
Pritine GNPs/E-51
fGNPs/E-51
Fig. 5. Mass fraction and surface functionalization of GNPs influencing on the
thermal conductivities of the nanocomposites.
100 200 300 400 500 600 700 800
60
65
70
75
80
85
90
95
100
300 350 400 450 500 550 600 650 700 750 800
96.0
96.5
97.0
97.5
98.0
98.5
99.0
99.5
100.0
Weight of loss / %
Temperature / oC
Pristine GNPs
fGNPs
Weight of loss / %
Temperature / oC
Pristine GNPs
fGNPs
275oC
Fig. 4. TGA curves of the pristine GNPs and fGNPs.
18 J. Gu et al. / International Journal of Heat and Mass Transfer 92 (2016) 15–22

Both the flexural strength and impact strength of the nanocom-
posites are increased up to 0.5 wt% incorporation, but decreased
with excessive addition of GNPs. Compared with those of pristine
E-51 (flexural strength for 106.2 MPa and impact strength for
13.6 kJ/m
2
), the maximum flexural strength and impact strength
of the fGNPs/E-51 nanocomposite with 0.5 wt% fGNPs is improved
to 133.7 MPa and 20.8 kJ/m
2
, increased by 25.8% and 52.9%,
respectively.
Appropriate addition of GNPs (0.5 wt%) can effectively transfer
stress, cause shear yield and prevent the crack propagation, finally
to improve the mechanical properties of the GNPs/E-51 nanocom-
posites. However, with the excessive addition of GNPs, more inter-
facial defects and stress concentration points are easily introduced
into the E-51 matrix, finally to decrease the mechanical properties
of the nanocomposites.
Furthermore, for a given GNPs loading, the surface functional-
ization of GNPs (fGNPs) can further increase the mechanical prop-
erties of the nanocomposites. The reason is that the interfacial
compatibility of fGNPs and E-51 matrix is improved. Meanwhile,
epoxy group of KH-560 molecules on fGNPs’ surface can react with
E-51 matrix, further to enhance the interface bonding strength
between fGNPs and E-51 matrix, finally to improve the mechanical
properties of the nanocomposites.
Fig. 8 shows SEM morphologies of impact fracture for pristine
fGNPs/E-51 nanocomposites and fGNPs/E-51 nanocomposites. For
a given GNPs loading, the inner defects in the fGNPs/E-51
nanocomposites are decreased obviously (Fig. 8b’ and c’). It
reveals that, compared with that of GNPs, fGNPs have relatively
better interfacial compatibility with E-51 matrix, which is
benefit for decreasing the inner defects, finally to increase the
mechanical properties of the nanocomposites. It is also
consistent with the results for the mechanical properties of the
nanocomposites.
3.4. Thermal properties of the nanocomposites
Fig. 9 shows the DSC curves of pristine E-51 and the
nanocomposites.
The Tg values of the GNPs/E-51 nanocomposites are increased
firstly, but decreased with the excessive addition of GNPs. The rea-
son is that, one hand, the addition of GNPs can effectively limit the
movement of molecular chains, to increase the Tg values of the
GNPs/E-51 nanocomposites. On the other hand, GNPs play a role
of effective physical cross-link point inner E-51 matrix [27]. And
the proportion of such physical cross-link section in whole E-51
matrix is increased with the increasing addition of GNPs. However,
the strength from physical cross-link role is lower than that of
chemical bond from chemical cross-link role, therefore, the corre-
sponding Tg values of the GNPs/E-51 nanocomposites are
decreased. When the mass fraction of GNPs is less than 0.5 wt%,
the influence of the former is superior to that of the latter. On
the contrary, the influence of the latter is superior to that of the
former when the mass fraction of GNPs is more than 0.5 wt%.
Meantime, for a given GNPs loading, compared with those of
pristine GNPs/E-51 nanocomposites, the fGNPs/E-51 nanocom-
posites possess higher Tg values. The reason is that the epoxy
group of KH-560 molecules on fGNPs’ surface can react with
E-51, further to enhance the interface bonding strength between
fGNPs and E-51 matrix, finally to increase the Tg values of the
fGNPs/E-51nanocomposites.
TGA curves of pristine E-51 and the fGNPs/E-51 nanocompos-
ites are presented in Fig. 10. And the corresponding characteristic
thermal data of pristine E-51 and the fGNPs/E-51 nanocomposites
are listed in the Table 5. The corresponding weight loss tempera-
tures of the fGNPs/E-51 nanocomposites are all increased with
the increasing addition of fGNPs at the same weight loss stage
(5 wt% and 30 wt%). The corresponding heat-resisting index is
192 °C (pristine E-51), 195 °C (0.5 wt% fGNPs), 199 °C (10 wt%
fGNPs), 200 °C (20 wt% fGNPs) and 203 °C (30 wt% fGNPs),
respectively. It indicates that the thermal stabilities of the fGNPs/
E-51 nanocomposites are gradually improved with the increasing
addition of fGNPs. The reason is that, compared with that of
pristine E-51, fGNPs has more excellent thermal conductivity,
which can be easier to absorb external thermal energy. Moreover,
the better interfacial compatibility between fGNPs and E-51 matrix
can represent a good mix of fGNPs and E-51 matrix, which can also
enhance the thermal stabilities of the fGNPs/E-51 nanocomposites.
Meanwhile, the corresponding residual mass
x
values of pristine
E-51 and the fGNPs/E-51 nanocomposites are 6.3%, 7.2%, 12.5%,
19.0% and 23.1% respectively, which also reveals the physical role
of fGNPs to E-51 matrix.
0 5 10 15 20 25 30
6
9
12
15
18
21
Impact strength / (kJ/m2)
Mass fraction of GNPs / %
Pristine GNPs/E-51
fGNPs/E-51
(a)
0 5 10 15 20 25 30
60
75
90
105
120
135 Pristine GNPs/E-51
fGNPs/E-51
Flexural strength / MPa
Mass fraction of GNPs /%
(b)
Fig. 7. Mass fraction and surface functionalization of GNPs influencing on the
mechanical properties of the nanocomposites.
Table 4
Elements and contents of white substances on the fracture surface of the fGNPs/E-51
nanocomposites.
Element Weight/%
C 93.82
O 4.15
Si 2.03
Total 100.00
J. Gu et al. / International Journal of Heat and Mass Transfer 92 (2016) 15–22 19

Fig. 8. SEM morphologies of impact fracture for pristine GNPs/E-51 nanocomposites and the fGNPs/E-51 nanocomposites.
20 J. Gu et al. / International Journal of Heat and Mass Transfer 92 (2016) 15–22

4. Conclusions
Static precipitation, XPS, FTIR and TGA analyses reveal that
KH-560 molecules have been grafted on the GNPs’ surface.
Compared with those of GNPs/E-51 nanocomposites, all the
fGNPs/E-51 nanocomposites possess better thermal conductivities
and mechanical properties. The thermal conductivities of the
fGNPs/E-51 nanocomposites are increased with the increasing
addition of fGNPs, and the corresponding thermally conductive
coefficient of the fGNPs/E-51 nanocomposites is improved to
1.698 W/mK (higher than that of GNPs/E-51 nanocomposite for
1.350 W/mK) with 30 wt% fGNPs, 8 times higher than that of pris-
tine E-51 matrix (0.201 W/mK). Both the flexural strength and
impact strength of the fGNPs/E-51 nanocomposites are optimal
with 0.5 wt% fGNPs. Compared with that of pristine E-51 matrix,
the maximum flexural strength and impact strength of the
fGNPs/E-51 nanocomposite with 0.5 wt% fGNPs is increased by
25.8% and 52.9%, respectively. Meanwhile, with the increasing
addition of fGNPs, the Tg values of the fGNPs/E-51 nanocomposites
are increased firstly, but decreased with the excessive addition of
GNPs. Furthermore, the thermal stabilities of the fGNPs/E-51
nanocomposites are also improved gradually with the increasing
addition of fGNPs. The surface functionalization of GNPs (fGNPs)
is helpful for further improving the thermal conductivities and
mechanical properties of the fGNPs/E-51 nanocomposites by min-
imizing interfacial thermal resistance and improving interfacial
compatibility between fGNPs and E-51 matrix.
Conflict of interest
None declared.
Acknowledgments
The authors are grateful for the support and funding from the
Foundation of National Natural Science Foundation of China
(Nos. 51403175 and 81400765); Shaanxi Natural Science Founda-
tion of Shaanxi Province (Nos. 2015JM5153 and 2014JQ6203);
Space Supporting Fund from China Aerospace Science and Industry
Corporation (No. 2014-HT-XGD); Aerospace Science and
Technology Innovation Fund from China Aerospace Science and
Technology Corporation, and the Fundamental Research Funds
for the Central Universities (No. 3102015ZY066).
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50 75 100 125 150 175
30wt% fGNPs/E-51
30wt% GNPs/E-51
20wt% fGNPs/E-51
20wt% GNPs/E-51
10wt% fGNPs/E-51
10wt% GNPs/E-51
0.5wt% fGNPs/E-51
0.5wt% GNPs/E-51
Pristine E- 51
Heat flow / (w/g)
Temperature / oC
Exo
Fig. 9. DSC curves of the pristine E-51 and the fGNPs/E-51 nanocomposites.
100 200 300 400 500 600 700 800
0
10
20
30
40
50
60
70
80
90
100
Temperature / oC
Weight of loss / %
Pristine E-51
0.5 wt% fGNPs/E-51
10 wt% fGNPs/E-51
20 wt% fGNPs/E-51
30 wt% fGNPs/E-51
Fig. 10. TGA curves of pristine E-51 and the fGNPs/E-51 nanocomposites.
Table 5
TGA characteristic thermal data of the pristine E-51 and the fGNPs/E-51
nanocomposites.
Samples Temperatures
for weight loss/°C
Heat-resistance
index
*
/°C
x
/%
5 wt% 30 wt%
Pristine E-51 367 403 192 6.3
0.5 wt% fGNPs/E-51 369 405 195 7.2
10 wt% fGNPs/E-51 372 415 199 12.5
20 wt% fGNPs/E-51 375 418 200 19.0
30 wt% fGNPs/E-51 376 422 203 23.1
T
Heat-resistance index
¼0:49 ½T
5
þ0:6ðT
30
T
5
Þ (1) [13], where T
5
and T
30
is corre-
sponding decomposition temperature of 5% and 30% weight loss, respectively.
*
The sample’s heat-resistance index was calculated by Eq. (1).
J. Gu et al. / International Journal of Heat and Mass Transfer 92 (2016) 15–22 21

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