Study on the curing reaction kinetics of a novel epoxy system

Article abstract of DOI:10.1039/c6ra25120j

The anhydride curing agent of 3,6-enodro-1,2,3,6-tetrahydrophthalic anhydride (OBPA) and the reactive epoxy diluent of furfuryl glycidyl ether (FGE) were prepared and characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H NMR). The curing reaction kinetics process of an EP/OBPA/FGE epoxy system was studied by non-isothermal DSC methods. The parameters of the kinetics were calculated using the Kissinger model, Crnae model, Ozawa model and β-T (temperature-heating speed) extrapolation, respectively. In addition, the effect of FGE on the thermomechanical properties (glass transition temperature) and mechanical properties (flexural strength and the tensile strength) in the EP/OBPA/FGE were studied, indicating that when the content of FGE was 10 wt% the epoxy system reaches the best mechanical properties.

Full text of DOI:10.1039/c6ra25120j

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Study on Curing Reaction Kinetics of a Novel Epoxy System
Jiheng. Ding,a Wanjun. Penga,b , Ting. Luoa,b, and Haibin. Yua
The anhydride curing agent of 3,6-enodro-1,2,3,6-tetrahydrophthalic anhydride (OBPA) and the reactive epoxy diluent of
furfuryl glycidyl ether (FGE) were prepared and characterized by fourier transform infrared spectroscopy (FTIR) and
nuclear magnetic resonance (1H NMR). The curing reaction kinetics process of EP /OBPA / FGE epoxy system was studied
by non-isothermal DSC methods. The parameters of kinetic were calculated using the Kissinger model, Crnae model,
Ozawa model and β-T (temperature-heating speed) extrapolation, respectively. In addition, the effect of FGE on the
thermomechanical properties (glass transition temperature) and mechanical properties (flexural strength and the tensile
strength) in the EP / OBPA / FGE were studied, indicating that when the content of FGE was 10 wt% the epoxy system
reaches the best mechanical properties.
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Keywords: Furfuryl
glycidyl ether; epoxy coating;
curing reaction; kinetics
process; mechanical
properties
costs or in environmental responsibility [6-11].
Introduction
Reactive epoxy diluents is a kind of compound with low viscosity
can dissolve or disperse into film material, reduce the viscosity of
Epoxy resin has excellent mechanical properties, bonding properties,
electrical insulation, strong mechanical properties, and a small
curing shrinkage and other advantages in physical and chemical
properties, which is widely used in chemical industry,
transportation, aerospace fields. Bisphenol A epoxy resin is one of
the most widely used epoxy resin, which accounts for about 80% of
the whole epoxy resin system and often widely used in the
manufacture of industrial coatings, adhesives and electronic panels
etc,[1-5].
epoxy resin, and can be involved in the process of resin curing
reaction, forming the non-volatile component and stay in the curing
system. It’s well know that phenyl glycidyl ether, benzyl glycidyl
ether, ortho methyl phenyl glycidyl ether, ethylene glycol diglycidyl
ether, and butyl glycidyl ether are the commonly used for epoxy
diluents, however, because of small molecules containing aromatic
glycidyl ether has the potential carcinogenic effects, and the
aliphatic glycidyl ether with shortcomings to reduce rigidity, heat
resistance and mechanical strength for epoxy resin, which limited
their application in epoxy systems. In view of the above results, the
preparation of bio-based reactive epoxy diluents has gradually
become a hot spot in the field of epoxy diluents [12-13]. Hu et al.
synthesized the 1,4-Bis[(2-oxiranylmethoxy)methyl]-furan (BOF),
which is a promising to substitute the petroleum-based 1,4-bis[(2-
oxiranylmethoxy)methyl]-benzene (BOB) to bring about a vast
improvement in the thermodynamic properties of thermosetting
Generally, the bisphenol A type epoxy resin possesses high viscosity,
poor permeability and fluidity. In order to facilitate the process of
operation, it usually need to add large amounts of volatile organic
compounds (VOC) as its solvent or diluent for reducing the viscosity
and improving the fluidity of the epoxy resin. Ethanol, acetone,
toluene, xylene etc., are the most commonly used solvents for
epoxy resin, however, most of them are flammable, toxic or difficult
to clean, and may cause danger of explosion, what’s more, the use
of solvents not only caused a substantial loss of oil resources, but
also caused serious environmental pollution for living. Therefore, it
is very important to reduce the use of VOC whether in economic
resin[14]. Huang et al. reported that the bio-based maleopimarate
as an epoxy curing agent to replace the petrochemical-based
trimellitic anhydride [15]. Ma et al. synthesized a novel itaconic
acid based glycidyl ether, which has great potential to replace the
petroleum-based thermosetting glycidyl ether[16].
a.
Key Laboratory of Marine Materials and Related Technologies, Key
Furfural is an important renewable material, which mainly exists in
corncob, and as the main structure of the furan ring with high
mechanical rigidity can be comparable with the petroleum based
aromatic ring and fatty ring. So the furfural and its derivatives such
as furfuryl alcohol, furan and furoic acid are widely used in the
polymer domain. Furfuryl glycidyl ether (FGE Fig.1 a) is obtained by
Laboratory of Marine Materials and Protective Technologies of
Zhejiang Province, Ningbo Institute of Materials Technology and
Engineering, Chinese Academy of Sciences, Ningbo 315201, P. R. China.
College of Materials Science and Engineering, Hunan University,
Changsha 410000, P. R. China.
b.
c.
College of Chemistry and Chemical Engineering, Hunan Normal University,
Changsha 410081, P. R. China
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reaction from furfuryl alcohol and epichlorohydrin, where the the experiments. furfuryl alcohol (FA), provided by Hubei new
epichlorohydrin is the derivatives of glycerol, and furfuryl alcohol is materials Co. Ltd. Bisphenol A epoxy resin (EP), industrial grade (E-
from furfural, so FGE is a kind of bio-based epoxy monomer. There 44, the epoxy value is 0.46), provided by Zhejiang Anbang coating
is the conjugated ring in the molecular structure of FGE, which has Co. Ltd.; All other reagents were purchased from Aladdin and used
high flexibility, while not losing rigidity. The structure of FGE can not as received.
only solve the problem of rigidity and heat resistance of aliphatic Synthesis of FGE
epoxy diluent, and can improve the brittleness and poor impact
The FGE was synthesized through the route in the Table 1.
resistance of the aromatic epoxy diluent epoxy curing system.
Epichlorohydrin (117.5g, 1.31 mol) and tetrabutylammonium
Therefore, as a new type of epoxy reactive diluent, FGE is expected
hydrogen sulfate (4.11g, 3.5%) were added into a 500 mL three-
to replace the traditional aryl ring, such as phenyl ether or benzyl
necked round-bottom flask. The system temperature was kept in an
ether [17-18].
ice-water bath at 0 ◦C. the furfuryl alcohol ( 63 g, 0.64 mol) was
On the other hand, the compound of 3,6-oxygen bridge-
dropped into above the solution over a period of 30 min. Then
1,2,3,6- four hydrogen phthalic anhydride (OBPA, Fig.1 b) come
NaOH aqueous (140 mL, 50 wt %) was added into the mixture over
from the adducts of D-A reaction of furan and maleic anhydride,
a period of 60 min and controlled the system temperature was not
and its molecular structure contains benzene and furan ring with
more than 10 ◦C. After 3.5 h, crude product was washed by water
outstanding rigidity, therefore, it is expected to replace the
three times, and the organic layer was collected and dried by
traditional epoxy curing agent such as phthalic anhydride or
magnesium sulfate anhydrous for 24 h, and the solvent was
trimellitic anhydride become a renewable bio-based epoxy curing
removed using by a rotary evaporator. The refined product was
agent[19-25] .
obtained by chromatography on a silica gel column with mixed
In order to get rid of the use of VOC in epoxy resin system, We
solvent of ethyl acetate/hexane (5:1). Yield: ～82 %.
have done the following research: (1) Compounds FGE and OBPA
FAꢀ 1H NMR (400 MHz, d6ꢀDMSO): (δ, ppm) 7.37 (d, 1H), 6.31(d,
1H), 6.25 (t, 1H), 4.25(s, 2H); FGEꢀ 1H NMR (400 MHz, d6ꢀDCl3):
(δ, ppm) 7.43 (q, 1H), 6.35 (d, 1H), 6.39 (t, 1H), 4.55(s, 2H), 3.76
(q, 1H), 3.45(q, 2H), 2.81 (q, 1H), 2.62(quint, 2H), 2.59 (q, 1H);
were synthesized and were used as curing agent and reactive
diluent of epoxy resin, respectively. Here, we hoped that the
synthesized FGE could play dual roles in the epoxy composites,
namely it can not only be used as a solvent for dissolve OBPA, but
Synthesis of D-A adduct of OBPA
also as a diluent for epoxy resin. (2) the EP / OBPA / FGE curing
The OBPA was prepared according to the Diels–Alder reaction in the
system was prepared and its thermal and kinetic parameters of
Table 1. Maleic anhydride (20 g, 0.20 mol) was dissolved in ether
curing process was analyzed and calculated by the non-isothermal
(150 mL) at room temperature; furan (15 mL, 0.20 mol) was
DSC method, and the optimum curing temperature of the system
dropped into the above-mentioned solution for 6 h under magnetic
was determined by T-β extrapolation. What’s more, the mechanical
stirring. And then the product was filtered to collect the OBPA. The
proprieties of EP / OBPA / FGE were studied too. Up to now, the
filter cake washed with a small amount of ethanol three times and
bio-based diluent of FGE and curing agent of OBPA for epoxy resin
dried at 40 ℃ in a vacuum until constant weight. Yield: ～98%.
has never been reported.
OBPAꢀ 1H NMR (400 MHz, d6ꢀDCl3): (δ, ppm) 6.58 (q, 2H), 5.35
(q, 2H), 3.31 (s, 2H).
Prepared of EP/ OBPA /FGE polymer system
Most of the anhydride is solid, and it is needed to be mixed with the
resin in the appropriate temperature to overcome this limitation. In
this paper, we used FGE as a solvent for anhydride curing agents.
Fig. 1 The structures of (a) FGE and (b) OBPA
Firstly, OBPA (10 g) was dissolved in (3g ) of FGE at room
temperature for 10 min without any solvent. Then, the above-
mentioned solution and 0.33 g of curing accelerators of 1-methyl
imidazole were added in 20 g of epoxy resin at room temperature
Experimental
for 5 min. The resultant homogeneous mixture was degassed, and is
Materials
added to the aluminium crucible (～3mg), the DSC scans were
Table1.The synthetic route of OBPA and FGE
performed according to the setting of the heating rate, and the DSC
curves were recorded.
FGE
Preparation of cured EP/ OBPA /FGE polymer
The epoxy anhydride curing agent OBPA (10 g) and curing
accelerators of 1-methyl imidazole (0.33 g) were dissolved into a
certain amount of FGE, the mixture was added into EP (20 g) and
heated to 80 oC for 30 min under vacuum. The resultant
homogeneous compound was degassed, poured into a closed
silicone rubber mould and cured at the given temperature. The
OBPA
Furan, maleic anhydride, epichlorohydrine, and 1- methyl imidazole
were purchased from Aladdin Industrial Corporation, and were used
without further purification. Deionized water was used throughout
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curing temperature was selected based on the optimum The peaks at 3400 cm−1 and 3465 cm−1 are ascribed to O-H of FA
temperature from above the Dynamic test results.
and FGE. The FTIR results proved that the product of FGE possesses
both furan and oxirane rings, which is also the chemical structure of
the target material FGE.
Characterizations
The 1H-NMR characteristic peaks of the FGE was listed in Fig. 3(1).
The signals from 2.65 to 2.75 ppm were assigned to the protons in
the oxirane ring (designated as protons7), while those signals at
3.42–3.85 ppm were assigned to protons 5 of –CH2 in the oxirane
ring. The signal at 3.22 ppm was assigned to proto 6 of –CH adjacent
to the oxirane ring. The signals at 6.2–6.3 and 7.4 ppm
corresponding to protons 2, 3 and 1 in furan ring, respectively. In
addition, the signal at 4.5 ppm was assigned to proto of –OCH2 in
furan ring and it indicted that the protons 4 link the glycidyl ether
moiety to the furan ring. The signal at 7.28 ppm was assigned water
peak in the CDCl3 solvent.
The chemical structures of products were confirmed by FTIR and
1H–NMR spectras. The FTIR spectrum (KBr) was collected with a
Thermo Nicolet Nexus 6700 instrument. 1H–NMR spectra was
obtained at room temperature on a 400 MHz AVANCE Ⅲ NMR
spectrometer in DMSO and CDCl3 with tertramethylsilane as
internal reference. The DSC curves were obtained using a NETZSCH
DSC 214 instrument with the protection of nitrogen and the flow
rate was about 20mL /min. The scanning temperature of system
was set from 25 to 300 ℃ and the heating rates were set to β = 5,
10, 15, 20, 25 K /min. The glass transition temperature (Tg) was
measured by the NETZSCH DSC 214 instrument under nitrogen
atmosphere with the heating rate of 20 oC/min, the heating
temperature range from 25 to 200 oC. Bending and tensile
properties of samples were tested by the WDW-05 electronic
universal testing machine and the standards as follows: the bending
performances were tested according to the GB/T 2570-1995, the
tensile properties were tested following GB/T 2568-1995, the test
results to take the average of six samples.
O
O
O
O
4,5
1,2
3,6
O
O
O
Results and discussion
2,3
4
Synthesis and characterization of FGE
1
7
5
6
In this work, FGE was prepared according to one-step method from
epichlorohydrin and furfuryl alcohol, and the purity of FGE was up
to 99.7%. The chemical structure of FGE was firm by FTIR and 1H-
NMR.
Fig. 3 Proton-NMR spectrums for the FA, FGE and OBPA.
Synthesis and characterization of OBPA
The FTIR spectrum of OBPA was shown in Fig. 2 too. The peaks at
3150 and 3110 cm−1 belong to the stretching vibrations of C–H in
furan ring; and the peak at 1640 cm−1 belong to stretching vibration
of C=C in furan ring; the peak at 1725 cm−1 belong to stretching
vibration of COOCO in OBPA.
The 1H-NMR characteristic peaks of the OBPA were shown in Figure
3 (2). The signals from 3.25 to 3.65 ppm were assigned to the
protons 4 and 5 of -CH; those signals at 5.85 ppm were assigned to
protons 3 and 6 of –CH in the epoxy ring; and the signal at 6.32
ppm was assigned to protons 1 and 2 of C=C adjacent to the furan
ring. The signal at 2.52 ppm was assigned water peak in the DMSO
solvent.
1
The FTIR and H-NMR results proved that the chemical structure of
Fig.2 The FTIR spectra of FA, FGE, ETA, and EP/ OBPA /FGE.
the target material OBPA.
Prepared and characterization of EP/ OBPA /FGE
Fig. 2 shows the FTIR spectra of FGE. For FA, the peaks at 3150 and
3110 cm−1 belong to the stretching vibrations of C–H in furan ring;
the peak at 1508 cm−1 belong to stretching vibration of C-C in furan
ring; the peaks at 1100 cm−1, 1015 cm−1, and 755 cm−1 are the the
stretching vibrations of C–O, furan ring breathing and
monosubstituted furan ring, respectively. Compared to FA, the new
peaks at 3060 cm−1, 1259cm−1, 858cm−1, and 914 cm−1 are assigned
to stretching vibrations of C-H and C-O-C in oxirane ring for FGE.
From the Fig. 2,the peak of COOCO at 1725 cm−1 disappeared and a
new peak at 1775 cm−1 belonging to the stretching vibrations of
C=O was observed in EP/ OBPA/FGE. The peak at 1640 cm−1 belongs
to stretching vibration of C=C in furan ring. Moreover, the signals of
epoxy group at 914 cm−1 and O-H at 3450 cm−1 in EP and FGE
disappeared. Those results demonstrated that the reaction of EP,
OBPA, and FGE was completed.
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The DSC Characterization of EP/OBPA/FGE
occurred. In addition, the parameter of reaction series n is usually
Fig.4 shows the non-isothermal DSC curves of EP / OBPA / FGE used to measure the degree of complexity of the system curing
polymer system, and the kinetic parameters of the curing process reaction, and the curing kinetic equation for EP/OBPA /FGE system
including the heating rate (β)，the starting temperature (Ti), the can be calculated according to the value of n. In this study, the
peak temperature (Tp), and the peak end temperature (Tf) were Kissinger, Owaza and Crnae equations were used to obtain the
recorded and listed in Table 2.
linear relation diagrams of ln(β/T2p) and lnβ to 1/Tp, and then the
According to the chart, during the curing process of the non- curves were processed by linear fitting method. Finally, the values
isothermal of EP/OBPA/ FGE system, the characteristic temperature of the apparent activation energy Ea, the pre-exponential factor A
of Ti, Tp, and Tf increased with the increase of heating rate, and the and the reaction order n of the system were obtained through
exothermic peaks of curing reaction gradually became sharp, and above the analysis and calculation.
moved towards the direction of high temperature. According to the The curing kinetics models of epoxy system mainly including
analysis results, on the other hand, during the curing process of EP / Kissinger, Fly-Wall-Ozawa and Friedman-Reich-Levi equations, and
OBPA / FGE system, the thermal inertia and heat flux increased with the Kissinger and Fly-Wall-Ozawa equations are the most commonly
the increase of heating rate, and the difference in temperature used for kinetics, and they follow the Eq. 1. The Kissinger equation
caused by the thermal effect became larger, so the curing can be obtained by derivation and differential treatment to Eq. 1,
exothermic peak shifted to high temperature. What’s more, when and the Kissinger equation was shown in Eq. 2. Here, the value of
the heating rate of the system was low, the system has sufficient ln[df(α)/d(α)] is approximately 0, as a consequence the Eq. 2 can be
time to react, so the curing reaction of the system could also be further simplified to Eq. 3.
occurred at low temperature. In addition, the values of ΔH of the
d
α
n
（1）
= K
(
T
)(1− )
α
system gradually became smaller with the increase of heating rate,
indicting that the lower of the value of heating rate, the more
complete of the curing reaction of the system.
dt
β
AR
Ea
df
d
(
α
)
Ea
（2）
ln[ ] = ln[
]+ ln[−
]
−
α p
Tp2
(
α
)
RTp
β
AR
Ea
（3）
（4）
ln（ ）= ln（ ）−
Tp2
Ea
RTp
A =[
β
Ea exp
(
Ea / RTp
)
]/ RTp2
Where, the t represents time, min-1; R is the perfect gas constant,
and the value of 8.32144 J/ (mol.K); Ea is the apparent activation
energy, J/mol; A is the pre-exponential factor min-1; β is the heating
rate, K/min; Tp is the peak temperature, K.
Fig.4 Non-isothermal DSC curves of EP / OBPA / FGE system
Table 2 Characteristic temperature from DSC curves.
﹒
min-1)
Ti/K
Tp/K
Tf/K
β/ (K
5
345.15
419.15
488.15
10
348.15
433.15
493.15
15
20
354.15
360.15
439.15
445.15
515.15
530.15
25
372.15
450.15
551.15
The kinetic parameters of EP/OBPA/FGE system
The analysis and calculation of the curing reaction kinetic
parameters of EP/ OBPA /FGE polymer system have important
theoretical and practical significance for its application in industrial.
The value of apparent activation energy (Ea) can directly reflect the
degree of difficulty in the curing reaction of the system. And the
reaction can occur only when the energy of EP/ OBPA /FGE polymer
system is greater than Ea, otherwise the curing reaction will not be
Fig.5 The relation between (β/T2p) and 1/ Tp. of Kissinger(A), the
relation between ln β/ and 1/ Tp of Crnae (B), and The relation
between lg β and 1/ Tp of Ozawa (C).
Table 3 The kinetics parameters of curing reaction.
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-
ln[β.Tp
Lnβ /(K.min)-
Tp-1/K-1
A/min-1
β/ (K
﹒
polymer system fitted first order linear relation. The average value
2/(K.min)-1]
1
min-1)
of apparent activation energy Ea was 73.87 kJ/mol,
2.583×108
2.473×108
5
-10.467
1.609
2.303
0.00239
0.00231
10
-9.840
2.742×108
2.724×108
15
20
-9.462
-9.201
2.708
2.996
0.00228
0.00225
2.680×108
2.640×108
25
-9.000
3.219
0.00221
average
The linear relationship of ln(β/T2p) and 1/ Tp can be obtained
through the Eq. 3, and the curve was shown in Fig. 5 A. The values
of slope and intercept of curve were obtained by linear fitting to the
curve were -8703.74 and 10.30, respectively. The results were
calculated in the Eq.3, and the value of apparent activation energy
Ea was 72.37 kJ/mol. In addition, the Eq.3 was deformed into as the
Eq.4, and the values of pre-exponential factor A can be calculated
and obtained via the Eq.4 based on the value of Ea. The values of
pre-exponential factor A were listed in Table 3 and the average
value of A is 2.640×108 min-1.
Fig.6 The relation between α and reaction time of EP / OBPA / FGE
system under different temperatures.
Curing dynamic equation of EP/OBPA/FGE system
The cure reaction kinetics Eq.10 was obtained via combined Eq.1
and Eq.9, and the Eq.11came from the integral of Eq.10. The above
values of Ea, A and n were brought into the Eq.11, and the kinetic
equation of curing reaction process of the EP / OBPA / FGE polymer
system was finally obtained in Eq.12. The linear relationship
between α and t was obtained in Fig.6 by means of Eq.11.
According to the Eq.11 and Fig.6, the reaction temperature of EP /
OBPA / FGE polymer system was higher, the reaction time was
longer, and then the value of conversion rate α was greater.
According to the relevant researches, the reaction order n of the EP
/ OBPA / FGE polymer system can be obtained by the calculation of
the Crnae equation in Eq.5. Here, the value of Ea/nR is much larger
than that of 2Tp in the Crnae equation, so the Eq.5 can be simplified
into the form of Eq.6. The linear relationship of lnβ and 1/ Tp (Fig.5
B)can be gotten through the Eq. 6, and the values of slope and
reaction order n were obtained by linear fitting to the curve, they
were -9538.51 and 0.912, respectively.
d ln
β
（5）
= −
(
Ea / nR + 2Tp
)
d
(
1/Tp
)
（9）
(
K = Aepx − Ea / RTp
)
d ln
β
Ea
d
( )
α
( )
t
（6）
n
（10）
= −
= Aepx
(
− Ea / RT )(1− )
α
d
(
1/Tp
)
nR
d
1
Generally, the kinetic parameters of EP / OBPA / FGE polymer
system can also be solved by using the Ozawa model equation. And
because the curing reaction mechanism was set up in advance for
the Kissinger equation during calculation process, it tends to give
the experimental data a greater error, and the error can be avoided
by the Ozawa model. Therefore, the Ozawa equation is often used
to verify the value of apparent activation energy Ea obtained by the
Kissinger model. The Ozawa model is as follows:
（11）
（12）
1−n
α
α
(
t
)
=1−
=1−
[
1+
(
n −1
)
Aexp
(
− Ea / RT
) ]
t
(
t
)
[
1ꢀ6.5×104 exp
(
−8.88×103 /T
)
t 11.36
]
Where, K represents the rate constant of reaction, S-1; α is the
reaction progress, %; t is the reaction time, s; T is the reaction
temperature, K.
AEa
Ea
（7）
lg
β
= lg[
]− 2.315 − 0.4567
Rf
(
α
)
RTp
The curing process of EP/OBPA/PGE system
From the Fig.1, the curing temperatures of the EP / OBPA / FGE
polymer system were different with the increase of the heating rate,
and the peak temperatures were different during the whole curing
reaction process, and then this makes it difficult to determine the
curing temperature of the EP / OBPA / FGE polymer system in the
actual curing process. In order to obtain accurate and reliable system
characteristic curing temperature, the T-β extrapolation method was
used to obtain the curing temperature when the heating rate of β is 0
K/min.
According to the theory that the a values corresponding to each
exothermic peak of DSC curve is approximately equal at different
heating rates of β, the value of apparent activation energy Ea can be
obtained by fitting the Linear relationship between lgβ and 1/Tp as
shown in Fig. 5 C. The value of slope of the curve was -4140.24, and
the value of Ea was 75.37 kJ/mol. From the above results, the values
of apparent activation energy of Ea obtained by the Kissinger and
Ozawa equations were almost equal, which further proved that the
kinetic equation of curing reaction process of EP /OBPA /FGE
In this work, by recording the characteristic temperature of Ti, Tp,
and Tf of EP / OBPA / FGE polymer system at different heating
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rates, then the values of heating rate were used as the horizontal diluent FGE has little effect on the glass transition temperature of
coordinate, and the values of Ti, Tp, and Tf were used as the vertical the EP / OBPA system.
coordinate to get the linear relationship graphs, and the curves
were obtained and shown in Fig.7. The curves were fitted and the
following equations were obtained:
Ti =1.32β+336.1 R=0.965
Tp =1.48β+415.1 R=0.935
(13)
(14)
Tf =13.26β+466.6 R=0.930 (15)
Fig.8 The glass transition temperature (Tg): EP / OBPA / FGE-0
represents the system without any FGE; the EP / OBPA / FGE-5, EP /
OBPA / FGE-10 and EP / OBPA / FGE-15 stand for the systems with
FGE in the dosage of 5 wt%, 10 wt% and 15 wt%.
The mechanical properties
The Fig.9 shows the effect of FGE on the flexural properties and the
tensile properties of EP / OBPA systems. From the Fig.9, the flexural
strength of the EP / OBPA systems increased with the increase of
FGE, while the tensile strength increases first and then decreases
with the increase of the content of reactive diluents of FGE, and
reaches its maximum of 72.4 MPa with 10 wt% of FGE. It was found
that the conjugated ring in the molecular structure of FGE would
improve the tenacity of epoxy resin, but when the content of FGE
was more than 15 wt% , the tensile strength of EP / OBPA system
decreased due to the decrease of cross-linking density. Based on
the above results, 10 wt% of FGE in the EP / OBPA system
possesses better mechanical properties.
Fig.7 The extrapolation plots of β-T.
From the extrapolation of β-T results can be known, the peak
starting temperature was 336.1 K (62.95℃), the peak temperature
was 415.1 K ((141.95℃)), and the peak end temperature of was
466.6
K (193.45 ℃ ) of EP / OBPA / FGE polymer system,
respectively. The above temperatures correspond to the gel
temperature, curing temperature and post curing temperature of
EP / OBPA / FGE polymer system, and the curing conditions of this
system was that: firstly, from room temperature to 63℃slowly, and
then continue to heat up to 142℃ for constant temperature curing,
and finally to heat up to 194℃ for post curing.
According to the above results, although the parameters of curing
temperatures are not established for the system to determine the
exact curing time, and cannot be directly used as the curing process
of the system, it can be a necessary theoretical basis for the
formulation of the EP / OBPA / FGE system curing process.
The thermomechanical properties
In the present work, the curing process of EP / OBPA / FGE system
was cured at 80 ℃ for 2 h, and then at 150 ℃ for 5 h. The glass
transition temperature (Tg) was measured by the NETZSCH DSC 214
instrument under nitrogen and the results of the variation in Tg
were listed in Fig. 8. From the Fig.8, the value of Tg of the system
decreased with the increase of diluent FGE, and the value of of Tg
of EP / OBPA / FGE-0 just is 1.5 ℃ higher than the EP / OBPA / FGE-
15. Generally speaking, the glass transition temperatures of
different systems depend on their own cross-linking density and
chain flexible. Compared with stiff phenyl group in the epoxy resin,
the conjugated ring in the molecular structure of FGE has high
flexibility, while not losing rigidity. As the result, the addition of
Fig.9 The mechanical properties: A represents the system without
any FGE; the B, C and D stand for the systems with FGE in the
dosage of 5 wt%, 10 wt% and 15 wt%.
6 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C6RA25120J
Journal Name
ARTICLE
Eur. J.Lipid Sci. Technol. 2013, 115, 698.
19 Wang. R, Schuman. T, Vuppalapati. R. R, Chandrashekhara. K,
GreenChem, 2014, 16, 1871.
Conclusions
(1) The reactive diluent of FGE and curing agent of OBPA for epoxy
resin were synthesized successfully in present work. And their
structures were confirmed by FTIR and 1H NMR.
20 Song. J. W, Guo, R. Liu, J. B, Wang. B. T, Applied Chemical
Industry, 2015, 44, 559.
21 Crane. L. W, Polymer science, 1973,11, 533.
22 Zhao. L. F， Liu. Y, Xu. Z. D，Forestry Studies in China，2011,
13, 21.
23 Kim. S， Kim. H. J, International Journal of Adhesion ＆
Adhesives, 2005, 18,456.
(2) The kinetic equation of curing reaction process of EP / OBPA /
FGE polymer system fitted first order linear relation, the value of
pre-exponential factor A was 2.640×108 min-1, and the apparent
activation energy Ea was 73.87 kJ/mol.
24 Gustavo. B. A, Leonardo. G. P, Andre´. S. A, Ronaldo. C. F,
Marcelo. A. P, Paulo. C. M, Maria. A. G, Chem. Phys, 2011, 13,
21233.
25 Zhang. J. Y, Chen. S. J, Zhu. Z. Y, Liu. S. Y, Chem. Phys, 2014,
16,117..
(3) According to the results of DSC scanning curves and the
extrapolation of T-β method, the best cure condition of EP / OBPA /
FGE polymer system was that: firstly, it is heated up from room
temperature to 63℃ slowly, and then continued to 142℃ for
constant temperature curing, and finally heated up to 194℃ for
post curing.
(4) The effect of FGE on the thermomechanical properties (glass
transition temperature) and mechanical properties (flexural
strength and the tensile strength) of EP / OBPA / FGE were studied,
and EP / OBPA / FGE-10 (with 10 wt% of FGE) has the best
mechanical properties.
Acknowledgements
The research is financially supported by the National Natural
Science Foundation of China (Grant no. 21404112), China
Postdoctoral Science Foundation (Grant no. 2014M561798)
and Ningbo Natural Science Foundation (Grant no.
2015A610016).
Notes and references
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