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76 Polímeros: Ciência e Tecnologia, vol. 18, nº 1, p. 76-80, 2008
Autor para correspondência: Luiz A. F. Coelho, UDESC - Centro de Ciências Tecnológicas, Campus Universitário s/n, CP 631, Bairro Bom Retiro,
CEP: 89223-100, Joinville, SC, Brasil. E-mail: dma2lafc@joinville.udesc.br
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I
ity of the neat epoxy which makes the dispersion of these
finely divided materials very challenging.
In this context, the goal of this work is to study the effect
of acetone solvent on the curing process as well as on the
properties of epoxy matrices. Thus, acetone/epoxy solutions
of different acetone concentrations, namely 0.0, 7.0, 10.0 or
13.0 wt.%, were prepared and then subjected to a mild pro-
cessing route to remove acetone. Viscosimetric, thermogra-
vimetric, tensile and morphological tests were performed in
order to evaluate possible changes in the samples. In addi-
tion, Fourier transform infrared spectroscopy (FTIR) analy-
ses were also employed in the search for changes in their
molecular structure.
Experimental
Materials
The epoxy resin and the hardener used were araldite GY
251 (diglycidylether of bisphenol A, DGEBA, Huntsmann)
and aradur HY 956 (Huntsmann), respectively. Acetone
(Quimidrol, 99.5% purity) was the chosen solvent.
Methodology
A certain amount of acetone (7.0, 10.0, or 13.0% of the
resin weight) was added to the resin and the mixture was
simultaneously sonicated in a Sonics Vibration (500 W) and
magnetically stirred for an hour. The mixture was then sub-
jected to heating at 50 °C for an hour and conditioned under
vacuum for five hours. Finally, hardener was added to the
mixture with a 5:1 (w/w) epoxy resin:hardener ratio and ho-
mogenized. The curing process took place at room tempera-
Introduction
The addition of solvents to thermoset resins is a possible
route to decrease resin viscosity, allowing a better distribu-
tion of fillers including, more recently, carbon nanotubes
(CNTs)[1-3].
Although the use of a solvent is beneficial to filler dis-
persion, it originates difficulties related to solvent removal
and the effect of residual solvent on resin characteristics.
Thus, the optimal, i.e. minimum, amount of solvent must
be identified and used, since even a small amount of sol-
vent left on the matrix may be responsible for hindering the
cross-linking process, being deleterious to the mechanical
properties of the resin.
Lau et al.[4] studied how traces of solvent may alter the
epoxy cross-linking process. The authors demonstrated that
the boiling point of solvents may be used as an attempt to
establish a trend regarding the effect on thermal and me-
chanical properties of epoxy. The influence of the solvent
was ultimately attributed to the different amount of unre-
acted epoxide groups and the extent of cure reaction. Hong
and Wu[5] studied the influence of different solvents on the
curing process of epoxy and dicyandiamide. According
to these authors, differential scanning calorimetry (DSC)
analyses revealed that the presence of solvent in the epoxy
resin results in lower curing exotherm, initial curing rate,
reaction rate, reaction order and glass transition tempera-
ture. They also found the most significant changes for the
solvents with higher boiling temperature.
Nevertheless, it is important to bear in mind that the
use of a solvent is very important as a way to adequately
prepare nanocomposites using CNTs as fillers in epoxy
matrices[4,6,7]. This is a necessary step due to the high viscos-
The Effect of Acetone Addition on the Properties of Epoxy
Marcio R. Loos, Luiz Antonio F. Coelho, Sérgio H. Pezzin
Centro de Ciências Tecnológicas, UDESC
Sandro C. Amico
DEMAT, PPGEM, UFRGS
Abstract: In this work, a varied amount of acetone was employed to dissolve an epoxy resin and then a route was followed
to remove the acetone, simulating a frequently used method to disperse nanofillers in thermoset matrices. Analyses were
then carried out to address the influence of residual acetone on the curing process and on the epoxy properties. The results
showed a detrimental effect on the mechanical properties of the cured epoxy due to the presence of residual acetone and
also a less brittle-like fracture of the specimen. Fourier transform infrared spectroscopy and thermogravimetric analyses
were additionally used to characterize the cured resins and have also indicated the presence of a small amount of acetone.
Nevertheless, rheological measurements indicated that 10.0 wt.% acetone addition on the resin causes a significant decrease
in viscosity (around 50%) which may promote a better dispersion of nanofillers.
Keywords: Acetone, epoxy, curing process, mechanical and physical properties.
Loos, M. R. et al. - The effect of acetone addition on the properties of epoxy
Polímeros: Ciência e Tecnologia, vol. 18, nº 1, p. 76-80, 2008 77
acetone appears to show a slightly lower viscosity than the
other samples for all shear rates tested.
Infrared spectroscopy
The FTIR spectra can provide information regarding
changes in the molecular structure of the samples through
the displacement, widening, appearance or lack of bands. As
can be seen in Figure 2 for the various solutions in uncured
state, the bands are quite similar, indicating that the use of
acetone does not appear to change the chemical structure of
the epoxy, similar to what has been suggested by Lau[4].
The peaks specifically related to acetone[9,10],
1708-1715 cm-1 (stretching of the C=O), 1731-1737 cm-1
(stretching of the gas phase of the C=O) and 3000-3005 cm-1
(stretching of the C=H) could not be separately identified due
to superposition with epoxy related peaks, especially the ab-
sorptions due to the stretching of the C=O and the C=H, at
1725 and 3005-3055 cm-1, respectively[4,11].
The most characteristic absorptions of the uncured epoxy
include a band around 910-920 cm-1[12-14], due to the contrac-
tion of the C-C bond and the stretching of both C-O bonds,
and a shoulder at 858 cm-1, due to the stretching of one C-O
bond and contraction of the other C-O bond of the epoxide
group[4]. After curing, the former band decreases in intensity,
shifts to higher values and may even split, whereas the shoul-
der disappears. Another reported feature of the cured epoxy
may include the appearance of a band around 1650 cm-1 re-
lated to the formation of an imino group. A full list of epoxy
infrared absorptions may be found in the work of Lau[4].
The FTIR may give more insight into the role of acetone
and for that, the band between 910-920 cm-1, was chosen as
the reference band. Comparing the spectra of the cured and
uncured resin, without acetone (Figure 3), it can be seen that
the reference band disappears if the epoxy is fully cured. On
the other hand, this band still remains for the samples with
acetone, although it has been shifted from 910 to 925 cm-1
and decreased in intensity, compared to the uncured curve.
ture for 24 hours under continuous vacuum. Samples without
acetone, called 0.0 wt.% of acetone, were also prepared for
comparison, using the same mixture and curing procedure.
Sample characterization
The viscosity of the epoxy/acetone mixtures was mea-
sured with the aid of a cone/plate apparatus (Brookfield CAP
2000). Thermogravimetric analyses (TGA) were conducted in
a Netzsch (STA 449C) equipment, heating the samples from
15 to 900 °C at a heating rate of 10 °C/min under nitrogen
atmosphere. Fourier transform infrared spectroscopy (FTIR)
analyses were conducted in a Perkin-Elmer Spectrum One B
equipment with a resolution of 4 cm-1, from 4000 to 650 cm-1,
on transmission mode.
Tensile tests, according to ASTM D638, were performed
in a Universal Testing Machine Emic DL 3000, with a 500
kgf load-cell and a 5 mm/min cross-head speed. Morphologi-
cal characterization of the fractured surface of the samples
was carried out via scanning electron microscopy - SEM
(equipment Zeiss DSM 940 A at 15 kV).
Results and Discussion
Viscosity
The viscosity of the various epoxy/acetone solutions at
50 °C is shown in Figure 1. The 0.0 wt.% acetone (neat resin)
curve shows a slight tendency to pseudoplastic behavior, that
is the viscosity decreases with shear rate, whereas no clear
trend was observed for the epoxy/acetone solutions in the
studied range of shear rates and the small variation in viscos-
ity appears to be within the experimental error and/or related
to some volatilization of acetone during the experiment.
Nevertheless, comparing the neat epoxy with the other
samples, it can be seen that the addition of acetone decreas-
es, in up to 50%, the viscosity of the resin, what is expected
considering that the solvating effect of the solvent weaken
inter-chain interactions[8]. Besides, the solution with 10% of
0.0 wt.%
7.0 wt.%
10.0 wt.%
13.0 wt.%
1000 2000 3000 4000 5000 6000 7000
Shear rate (s-1)
Viscosity (mPa.s)
160
140
120
100
80
60
Figure 1. Viscosity of the samples with 0.0, 7.0, 10.0 and 13.0 wt.% of
acetone under different shear rates.
Wave number (cm-1)
4000 3500 3000 2500 2000 1500 1000
%T
0.0 wt. %
7.0 wt. %
10.0 wt. %
13.0 wt. %
Figure 2. FTIR spectra obtained for the samples with 0.0, 7.0, 10.0, and
13.0 wt.% of acetone - uncured resin.
Loos, M. R. et al. - The effect of acetone addition on the properties of epoxy
78 Polímeros: Ciência e Tecnologia, vol. 18, nº 1, p. 76-80, 2008
possibly due to the decomposition of lower molecular weight
material, and the other one, between 290-490 °C (peak at
368 °C in Figure 4b), referring to the degradation of the resin
material[17] of higher molecular weight formed during cur-
ing.
However, the TG curves obtained for the epoxy with ac-
etone (Figure 4a) have shown a different profile. There is an
initial small weight loss, between 40-140 °C (peak at 89 °C
in Figure 4b), corresponding to the evaporation of trapped
solvent, a similar behavior to that reported by Sharmim[18] for
epoxy/dimethylsulphoxide solution. The derivative TG plot
clearly shows the presence of this extra peak for the acetone
cured epoxy resins.
Figures 4a,b also indicate that the presence of acetone
causes a increase in the intensity of the peak at 240 °C.
Besides, the weight loss in the range 160-290 °C increases
from 5.2%, for the neat resin, to around 9.7% for the other
samples, which suggests that there is comparatively more
material on lower molecular weight chains, which may un-
dergo thermal degradation sooner. This can be attributed to
the incomplete cure of the resin due to the presence of residu-
al acetone, that affects the curing kinetics and, consequently,
the structure of the epoxy resin[12]. The presence of acetone
is likely to decrease the degree of cross-linking, increasing
the chain molecular mobility, ultimately lowering the glass
transition temperature[5].
Tensile properties
Table 1 presents the tensile testing results of the differ-
ent samples. It can be seen that the presence of acetone re-
sulted in a decrease in Young’s modulus, tensile strength and
elongation at break of the epoxy resin. This effect was more
pronounced for resins prepared with a higher acetone con-
tent, reaching a 16-21% decrease in these properties for the
13.0 wt.% acetone sample. The decrease in Young’s modulus
is particularly interesting in ratifying the findings regarding
the mentioned lower degree of crosslinking of the resins in
which acetone had been added. Mondragon[15] also found for
a DGEBA epoxy resin that the presence of a small amount of
solvent (in their case CH2Cl2) at the beginning of the curing
reaction, even if they are later lost by evaporation, have a
measurable effect on curing kinetics and Tg of the resin due
to a modification of the network structure.
The decrease in tensile strength and elongation at break
may be related to the presence of weakly bonded acetone rich
areas of the resin which may act as stress concentration points.
This is an indication that there is acetone left on the epoxy
resin which has affected the cross-linking process, decreas-
ing the conversion degree of reactive groups[4,15].
Thermogravimetry
Thermogravimetric analysis (Figure 4) of the neat cured
epoxy[16] has shown two major weight loss events in Figure 4a,
the first, between 160-290 °C (peak at 240 °C in Figure 4b),
%T
1900 1700 1500 1300 1100 900 700
Wave number (cm-1)
13.0 wt. %
10.0 wt. %
7.0 wt. %
0.0 wt. %
0.0 wt. % - uncured
Figure 3. FTIR spectra obtained for the samples with 0.0, 7.0, 10.0, and
13.0 wt.% of acetone after the curing process.
100
80
60
40
20
0
0 200 400 600 800
Temperature (°C)
Weight (%)
0.0 wt. %
7.0 wt. %
10.0 wt. %
13.0 wt. %
(a)
0
-2
-4
-6
-8
-10
-12
0 200 400 600 800
Temperature (°C)
Deriv weight (%/min)
0.0 wt. %
7.0 wt. %
10.0 wt. %
13.0 wt. %
(b)
Figure 4. a) TG; and b) DTG curves for the samples with 0.0, 7.0, 10.0 and
13.0 wt.% of acetone.
Table 1. Tensile properties of the samples.
Acetone
(wt. %)
Young´s
modulus
(GPa)
Tensile
strength
(MPa)
Elongation
at break
(%)
0.0 2.5 + 0.3 42.8 + 2.0 2.8 + 0.4
7.0 2.3 ± 0.1 40.8 ± 1.0 2.5 ± 0.4
10.0 2.2 ± 0.4 38.7 ± 0.8 2.5 ± 0.4
13.0 2.1 ± 0.2 34.4 ± 3.0 2.2 ± 0.4
Loos, M. R. et al. - The effect of acetone addition on the properties of epoxy
Polímeros: Ciência e Tecnologia, vol. 18, nº 1, p. 76-80, 2008 79
less brittle-like fracture is observed. This may be compared
to a less extent to the effect of moisture on saturated epoxy
specimens, which show a transition to ductile behavior due
to moisture-induced plasticization, i.e. from a brittle fracture
mechanism such as crazing to a ductile mechanism such as
bulk shear yielding[20]. This could explain some near circu-
lar or ellipsoid patterns left on the fractured surface of the
13.0 wt.% acetone sample.
Furthermore, no apparent porosity was found in any of
the micrographs taken, indicating that the difference in me-
chanical properties is indeed a consequence of alterations in
the characteristics of the resin material.
Conclusions
The influence of the presence of residual solvent, namely
acetone, on the characteristics of an epoxy resin was studied.
It may be concluded that care must be exercised in order to
ensure that all solvent is removed before curing, otherwise
the cross-linking process is altered, leading to significant
changes in physical and mechanical properties, for instance
the Young´s modulus, even if only a small amount of solvent
is left on the matrix. The molecular strucuture of the cured
resin has also been affected, as detected by FTIR analyses,
and SEM micrographs showed a less brittle-like fracture for
the material to which acetone had been added. Thermal deg-
radation has also been affected by the acetone.
Nevertheless, a 50% reduction in viscosity due to solvent
solvating of the DGEBA molecules was found when 10 wt.%
of acetone was added to the epoxy resin, which is very bene-
ficial to processes where finely divided fillers are to be incor-
porated and dispersed into highly viscous polymer resins as a
consequence of a stirring process, helping defining more suit-
able conditions for the preparation of epoxy nanocomposites
with carbon nanotubes when following this solvent route.
Acknowledgments
The authors would like to thank CAPES-PROCAD (Proj-
ect 0303054) for the financial support and for the scholarship
to Mr. M. R. Loos.
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Reenviado: 09/09/07
Aceito: 14/09/07
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