World Journal Of Engineering
The Effects of Functionalized Graphene Sheet on
The Properties of Poly(ethyl methacrylate)
Su Jin Han, Seong Min Oh, Hyung-il Lee, Han Mo Jeong*
Department of Chemistry, University of Ulsan, Ulsan 680-749, Korea
*
Corresponding Author. E-mail: hsjsjf@hanmail.net
stirred at 25 ℃. After 24 h, the mixture was poured into 3
L of distilled water. The GO was filtered and washed with
distilled water until the pH of the filtrate was neutral,
dried in a vacuum oven at 100 ℃, and then pulverized
and screened with a 100 mesh sieve to obtain fine
particles. An elemental analysis showed that the
composition of the GO was C10O3.55H1.32.
To obtain FGS, the dried GO was charged in a quartz tube
and flushed with nitrogen for 5 min, and then the quartz
tube was quickly inserted into a furnace preheated to
1100 ℃ and kept in the furnace for 1 min to split the GO
into individual sheets through the evolution of CO2.6
Elemental analysis showed that the composition of FGS
was C10O0.76H0.91.
Introduction
Recently, it has been reported that the mixture of few
layers graphene sheets can be prepared in bulk quantity
from sufficiently oxidized graphite oxide by rapid
pyrolysis. This is possible because the rapid heating at
high temperatures evolves gases, such as CO2, from the
chemical decomposition of oxygen-containing functional
groups in the GO and the instantaneous pressure
generated by the gases can exfoliate the GO.6 These
exfoliated sheets, which are called functionalized
graphene sheets (FGSs), have an affinity for polar
solvents and polymers, because some of the oxygencontaining groups, such as epoxy or hydroxyl groups,
remained even after thermal treatment.1
Some researchers have utilized the functional groups of
GO to prepare the graphenes grafted with polymers. 2-5
However, to the best knowledge of the authors, no paper
to date has investigated the grafting reaction onto
graphene during the radical polymerization of vinyl
monomers in the presence of graphene. Thus, in this
study, we prepared FGS/poly(ethyl methacrylate)
(PEMA) nanocomposites by both a physical mixing
method and by an in situ method, in order to examine the
grafting reaction. This paper reports the results and the
effect of the grafting reaction on the physical properties
of the FGS/PEMA nanocomposite.
FGS/PEMA Nanocomposite Preparation.
FGS/PEMA nanocomposites were prepared by two
different methods, an in situ method and a physical
mixing method. During the in situ method, ethyl
methacrylate (EMA) was polymerized in the presence of
FGS with 2,2’-azobisisobutyronitrile (AIBN) as a radical
initiator to make nanocomposites under a N2 atmosphere
at 65℃ for 6 h while stirring with a magnetic bar.
Prepared FGS/PEMA nanocomposites were crushed into
a powder and dried at 110℃ under a vacuum for 24 h to
remove low molecular weight components. In the
physical mixing method, FGS was dispersed in THF and
sonicated for 1 h at room temperature. This sonicated
mixture, about 1 wt% solid content, was fed into the 10
wt% PEMA solution in THF and agitated at 60℃ for 6 h.
The THF was evaporated at 110℃ under a vacuum for 24
h to obtain the nanocomposite.
The sample designation codes used in the Table, Figure,
and text give information about the preparation method
and the content of FGS in the nanocomposites. That is,
SC1 was made by an in situ method and contains 1.02
wt%
Experimental
Preparation of FGS.
The graphite oxide (GO) was prepared using the Brodie
method.6 In a typical experiment, a reaction flask with
200 mL fuming nitric acid was cooled to 0℃ in an ice
bath, and then 10 g of graphite powder was added to the
flask by stirring. Next, 85 g of potassium chlorate was
slowly added over 1 h, and the reaction mixture was
Table 1. Recipes for the Preparation of FGS/PEMA Nanocomposites and Their Characteristics.
Feed (by weight)
Content of FGS (wt%)
Polymerizaion
Yield (%)
Sample
Molecular
weight of PEMA
by TGA
Calculated from
polymerization yield
Mn
Mw
92.6
-
-
28,800
88,500
0.5
90.4
1.02
1.09
21,200
48,400
0.5
89.1
3.15
3.26
22,800
62,400
EMA
FGS
THF
AIBN
C0
100
-
400
0.5
SC1
100
1
400
SC3
100
3
400
403
World Journal Of Engineering
SC5
100
5
400
0.5
86.2
FGS, as shown in Table 1. MC1, MC3, and MC5 were
made by a physical mixing method and contain 1.02 wt%,
3.15 wt%, and 5.82 wt% FGS, respectively.
5.82
5.48
19,700
55,200
physical mixing method, showed that the interaction
between FGS and matrix PEMA molecules was enhanced
probably by the PEMA chains grafted on FGS.
Table 2 Residual Weights of FGS Washes after Thermal
Degradation.
Results and Discussion
The FGS/PEMA nanocomposites were dissolved with a
100-fold amount of THF; the dispersed FGS was then
filtered through 1-μm filter paper. The filtered FGS was
dispersed in a second 100-fold amount of THF, agitated
at room temperature for 24 h to wash out any PEMA
molecules adhered on the FGS, and then filtered again.
This washing operation was repeated up to five times.
Table 2 shows the TGA results of the FGS washes. As
described before, the residual weight at 700℃ shown in
Table 1 can be considered to be that of FGS, and the
weight reduction might have been caused by PEMA. The
data presented in Table 2 show that the amount of
adhered PEMA in the washed FGS is more than 30% by
weight, even after washing, although it decreases with
repeated washes. Our results in Table 2 show that the
physical interactions between FGS and PEMA molecules
are strong enough that they cannot be easily separated by
a solvent. The amount of adsorbed PEMA increased when
the nanocomposites were prepared by the in situ
polymerization method, as compared to those prepared by
the physical mixing method, as shown in Table 1. These
results indicate that the cohesion of PEMA molecules on
FGS was enhanced probably by grafting during the in situ
polymerization method.
The tensile storage modulus, E' measured by DMA is
shown in Figure 1, where one can see that E' is enhanced
by the reinforcing effect of FGS. This effect is more
evident in the samples prepared by in situ methods, as
compared to those by the physical mixing method. This
result indicates that the stress transfer from matrix
polymer to FGS, in the nanocomposites prepared by the
in situ method, is improved by the PEMA molecules
adhered on the FGS. In Figure 1, one can also see that the
enhancement of E' is more evident at the rubbery state
above the glass transition temperature (Tg), as compared
to that at the glassy state below Tg; similar results were
observed for polyurethane/clay nanocomposites7,8 and
poly(acrylonitrile)/clay nanocomposite.9 This evident
improvement at a temperature range above Tg can be
explained by the enhanced shear deformation of matrix
molecules and enhanced stress transfer to the rigid FGS,
due to the increased elasticity of the matrix at the
temperature range above Tg.10
Residue (%)
Sample
1st wash
3rd wash
5th wash
MC1
SC1
52.4
41.8
61.5
51.7
67.7
54.8
MC5
SC5
56.2
52.9
65.6
61.3
69.8
66.4
Fig 1. Tensile storage modulus of FGS/PEMA
nanocomposite.
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Conclusion
The results of TGA and FT-IR indicated that PEMA
molecules were grafted on FGS during radical
polymerization of EMA by AIBN.
The improvement of E' observed by DMA and the
increased η* and pseudo-solid behavior in the rheological
404