Fabrication and characterization of superparamagneticnanocomposites based on epoxy resin and surface-modifiedc-Fe2O3 by epoxide functionalization

Zahra Sekhavat Pour • Mousa Ghaemy

Received: 2 November 2013 / Accepted: 14 February 2014

� Springer Science+Business Media New York 2014

Abstract In this study, the effect of modified epoxide-

terminated c-Fe2O3 on the magnetic, mechanical, and

thermal properties of epoxy nanocomposite was investi-

gated. The c-Fe2O3 nanoparticles were prepared via a wet

chemical approach, surface modified with 3-glycidox-

ypropyltrimethoxysilane (GPTMS), and characterized by

particle size analyzer, XRD, FT-IR, and TGA techniques.

The catalytic effect of c-Fe2O3 on the cure reaction tem-

perature of epoxy/triethylenetetramine (TETA) was deter-

mined by differential scanning calorimeter (DSC). The

glass transition temperature (Tg) of nanocomposite con-

taining 5 wt% modified c-Fe2O3 increased slightly (12 �C),

while the initial decomposition temperature (TID) did not

show improvement. Transmission electron microscopy

(TEM) showed improvement in dispersion of surface-

modified c-Fe2O3 nanoparticles in the resin matrix. The

effect of interfacial bonding between modified c-Fe2O3 and

epoxy resin, via crosslink reactions, on the mechanical

properties of nanocomposite such as flexural and tensile

strength was studied, and the fractured surface of samples

was investigated by scanning electron microscopy (SEM).

Comparing with the mechanical properties of neat epoxy

resin, tensile, and flexural strength of 10 wt% modified

c-Fe2O3/epoxy nanocomposite increased 20 and 19 %,

respectively, while tensile and flexural strength of 10 wt%

unmodified/epoxy nanocomposite decreased slightly. The

saturation magnetization (Ms) of 5 wt% modified c-Fe2O3/

epoxy nanocomposites with superparamagnetic property

was approximately 80 % greater than that of unmodified

c-Fe2O3/epoxy nanocomposites.

Introduction

Incorporation of nanoparticles into polymer matrixes is a

good strategy for a simultaneous improvement of different

material properties. Mechanical and thermo-mechanical

properties are definitely higher in the case of nanosized filler

with respect to micron-sized dispersed [1–3]. It is well known

that the unique nanocomposite performance can be achieved

by homogenous dispersion of nanoparticles into polymer

matrix and avoiding the formation of agglomerates. Com-

posites consisting of epoxies as matrix material and nano-

particles as fillers have been in the focus of many

investigations [4–8]. Using appropriate surface modifiers

such as trialkoxysilanes not only leads to better dispersion of

nanofillers in the resin matrix but also causes formation of

chemical and physical interactions with polymer matrix and

improves electrical and thermo-physical properties of the

composites [9]. The effects of silane modification of nano-

particle surface on the cure kinetics of carbon nanofiber/

epoxy composite [10] and nanoclay/epoxy resin composite

[11] were investigated. Applications of magnetic nanoparti-

cles in polymeric matrix possess unique optical, electrical,

magnetic, and biochemical properties which are not found in

their bulk counterparts [12–16]. Then, interest in design and

development of these nanocomposites with superior magnetic

property continues to increase. However, due to large specific

surface area, high surface energy, and magnetization, mag-

netic nanoparticles tend to agglomerate to reduce their surface

energy. This is the main drawback of magnetic nanoparticle

application, synthesis, and processing, and strategies should

be designed to prevent nanoparticle aggregation [17]. Nano-

composites of Fe3O4/epoxy resin showed poor dispersion and

agglomerate formation even in low concentration of nano-

particles [18, 19]. Zhu et al. showed the saturation magneti-

zation (Ms) of Fe@FeO/epoxy nanocomposite with particle

Z. Sekhavat Pour � M. Ghaemy (&)

Polymer Research Laboratory, Department of Chemistry,

University of Mazandaran, Babolsar 47416-95447, Iran

e-mail: ghaemy@umz.ac.ir

123

J Mater Sci

DOI 10.1007/s10853-014-8114-6

loading of 20 wt% is 15.8 % of that of the pure nanoparticles,

while the coercivity increased after the nanoparticles were

dispersed in the epoxy matrix [20]. Gonzalez et al. [21]

observed well-dispersed magnetite nanoparticles modified

with oleic acid in epoxy matrix and superparamagnetic

behavior in both nanoparticles and nanocomposites. How-

ever, to the best of our knowledge, preparation and charac-

terization of magnetic nanocomposites with epoxy matrix

scarcely reported in the literatures especially for epoxide

functionalized c-Fe2O3/epoxy nanocomposite. The work

described in this paper deals with the synthesis and charac-

terization of nanocomposite containing functionalized c-

Fe2O3 bonded with epoxy resin matrix. Magnetic c-Fe2O3

nanoparticles were synthesized via a wet chemical approach

using iron(II) chloride tetrahydrate and iron(III) chloride, and

then were modified by surface epoxide functionalization

using 3-glycidoxypropyltrimethoxysilane (GPTMS). It was

expected that disperse ability of silane-modified c-Fe2O3 will

improve in the resin matrix, and nanocomposites with better

performance will be achieved. Therefore, the effect of mod-

ification of c-Fe2O3 nanoparticles on the composite perfor-

mance was investigated and compared with the unmodified c-

Fe2O3/epoxy composite and neat epoxy. In this process, the

cure reaction was studied by DSC; magnetic, mechanical, and

thermal properties of composites were measured by vibrating

sample magnetometer (VSM), tensile and flexural tests, and

thermal gravimetric analysis (TGA); and morphological

characteristics by SEM and transmission electron microscopy

(TEM).

Experimental section

Materials

The diglycidyl ether of bisphenol A (DGEBA) type epoxy

resin, (Epiran 6), was supplied by Khuzestan Petrochemical

Co. (Iran) with an epoxide equivalent weight of 187 eq/g.

Triethylenetetramine (TETA) with a purity of 99.5 % is an

aliphatic amine used as curing agent and was purchased

from Fluka (Germany). GPTMS as coupling agent and FeCl3(99 %), FeCl2�4H2O (98 %), HCl (37 %), and NH4OH

(25–30 %) were purchased from Merck (Germany).

Preparation of c-Fe2O3 nanoparticles

Magnetic c-Fe2O3 was prepared by wet chemical method

according to a previously reported procedure [22]. Iron(II)

chloride tetrahydrate and iron(III) chloride (Fe2?:

Fe3? = 1:2) were dissolved in 2 M hydrochloric acid. The

NH4OH solution (2 M) was added to this solution with

vigorous stirring at room temperature for 2 h, forming a

brown precipitate. The final pH was about 10. The brown

precipitate was separated from the solution by using a

magnet and rinsed several times with distilled water until the

pH reached 7.0. The brown c-Fe2O3 particles were dried at

60 �C overnight and then were crushed down by mortar.

Surface modification of c-Fe2O3 nanoparticles

Surface modification of c-Fe2O3 was performed as follows.

2 g of c-Fe2O3 nanoparticles was kept in a vacuum

chamber at 110 �C for 75 min and then dispersed in ace-

tone by stirring for 1 h at ambient temperature, and finally

was sonicated (Elma, TRANSSONIC T890) for 20 min.

Then, 1 g GPTMS (50 wt%) was gradually added to the

dispersed solution and stirred for further 24 h at ambient

temperature. Finally, it was centrifuged and the residue is

washed with acetone. The washing procedure was repeated

for three times, and the remained precipitate was dried in a

vacuum oven at 50 �C for 72 h. The grafting of GPTMS on

the c-Fe2O3 nanoparticles was confirmed by particle size

analyzer (PSA), TGA, and FT-IR.

Fabrication of c-Fe2O3/epoxy nanocomposites

Unmodified and modified c-Fe2O3 nanoparticles were dried

in a vacuum oven at 80 �C for 1 h and then were mixed with

epoxy at different weight percentages (1, 5, and 10 wt%).

The fabrication processes of c-Fe2O3/epoxy mixtures were

as follows. Unmodified and surface-modified c-Fe2O3

powders were dispersed in acetone (25 ml acetone per gram

of nanoparticles) before adding the epoxy, and the mixture

was ultrasonicated for 20 min. This particle-solvent dis-

persion was introduced to DGEBA resin slowly using

mechanical mixing. The mixture was then outgassed at

70 �C for 3–4 h to eliminate the remaining acetone. To

ensure that all solvent was removed, constituent weights

were monitored at all steps. Then, stoichiometric amount of

TETA as curing agent was added into the mixture and agi-

tated for 5–10 min by hand mixing. This mixture was poured

into pre-prepared casting mold and cured at room tempera-

ture for 24 h, and then postcured in a vacuum oven at 75 �C

and at 110 �C for 2 h and 1 h, respectively.

Measurements

The crystalline structure of c-Fe2O3 nanoparticles was char-

acterized by X-ray diffraction (Philips Analytical X-ray B.V.)

using Cu Ka (k = 1.54 A) radiation. FT-IR spectra of pris-

tine and modified c-Fe2O3 were recorded on a Bruker Vector

22 FT-IR spectrometer in the range of 400–4000 cm-1. To

determine the size distribution of pristine and modified

c-Fe2O3 particles, the prepared particles were dispersed in

distilled water, and measurements were performed using a

particle size analyzer (Scatteroscope I, Qudix, Korea).

J Mater Sci

123

A differential scanning calorimetry (DSC1 METTLER

TOLEDO, Switzerland) was employed to follow the progress

of cure reaction of epoxy/TETA and modified c-Fe2O3/

epoxy/TETA mixtures. About 10 mg of each sample was put

in an aluminum pan and heated from room temperature to

250 �C at a heating rate of 10 �C min-1 in nitrogen gas purge.

Then, the sample was cooled to ambient temperature and

scanned again up to 300 �C to determine the glass transition

temperature (Tg). A vibrating sample magnetometer (VSM)

(Kavir Magnetic Co. Iran) was used to evaluate the room

temperature magnetic parameter of the composites with an

applied field from -8000 to ?8000 Oe. In VSM, the sample

under study was kept in a magnetic field to be magnetized by

aligning the magnetic dipoles or the individual magnetic spins

of the magnetic particles along the direction of the applied

magnetic field. The stronger the applied field, the larger is the

magnetization. The tensile properties of the samples were

determined on dog-bone shaped samples according to ASTM

D 638 at room temperature using an Instron Universal Testing

Machine (Gotech Testing Machines Inc. U60). Dimensions of

specimen were chosen according to the type I of this standard

and a 2 mm/min cross-head speed was used. To measure

flexural properties, the three-point bend tests were performed

using a universal testing machine according to ASTM D 790.

The support span was 50 mm with a cross-head speed of

1 mm/min at room temperature. Five specimens of each

composition were tested to evaluate each of the mechanical

tests. Scanning electron microscopy (SEM) (Leo 1455 VP,

Germany) was used to evaluate the morphology of fractured

interfaces obtained from flexural test. Dispersion state of c-

Fe2O3 with and without modification was also examined by

SEM. Transmission electron microscopy imaging of the

nanocomposite films containing 1 wt% c-Fe2O3 particles was

performed using a TEM instrument (modelEM10C, Zeiss

Co.) with an accelerating voltage of 80 kV. Ultra-thin sec-

tions (*70 nm) of sample were prepared using ultramicro-

tome and were recovered on a copper grid. The thermal

stability of pristine and modified c-Fe2O3 nanoparticles,

cured samples of epoxy/TETA, and unmodified and modified

c-Fe2O3/epoxy nanocomposites was evaluated with TGA

(Rheometric Scientific, USA) from room temperature up to

600 �C with the heating rate of 10 �C min-1.

Result and discussion

Characterization of magnetic c-Fe2O3 nanoparticles

Figure 1 shows the X-ray diffraction pattern of the syn-

thesized c-Fe2O3 before modification. All the diffraction

peaks are in agreement with the pure phase of c-Fe2O3

(reference pattern code: 01-089-5892). The main peaks for

c-Fe2O3 are observed at 2h = 26.91 (d = 3.311), 30.39

(d = 2.939 A), 35.72 (d = 2.513 A), 43.47(d = 2.080 A),

53.52 (d = 1.710 A), 57.36 (d = 1.605 A), and 63.04�(d = 1.473 A) [13, 22]. The crystalline size of c-Fe2O3

nanoparticles was determined by measuring the full width

at half maximum (FWHM) using Scherrer Eq. (1):

D ¼ kk=b cos h ð1Þ

where D is the crystalline size for individual peak, k = 0.9

was used as Scherrer constant, k is the X-ray wavelength

(k = 0.154 nm), h is the Bragg angle, and b is FWHM. The

average estimated crystalline size is found to be about

13.19 nm. However, physical forces like van der Waals,

hydrogen bonding, and electrostatic interaction lead to an

agglomeration of nanoparticles. One of the useful ways to

overcome the agglomeration of nanoparticles is modification

of the surface with a coupling agent such as organofunctional

silanes [23]. The hydroxyl groups on the surface of nano-

particles react with silanes to prevent agglomeration and to

compatibilize the particles with the resin. Therefore, the size

distribution of c-Fe2O3 nanoparticles before and after sur-

face modification was investigated by the particle size ana-

lyzer (PSA). As can be seen in Fig. 2, the average size of

unmodified c-Fe2O3 particles in water phase is approxi-

mately 100 nm which is larger than those measured by TEM

technique (*20 nm). Particle size measurement by PSA

technique is carried out in water phase, thus some agglom-

eration can possibly occur due to high surface area and Van

der Waals forces between magnetic particles. After surface

modification with GPTMS, the mean particle size has been

reduced to a value of about 60 nm as a result of less

agglomeration. Therefore, silanization of c-Fe2O3 particles

surface reduces the Van der Waals forces and agglomeration

is prevented. Figure 3a shows the chemical reaction between

GPTMS and hydroxyl groups on the surface of c-Fe2O3. For

the purpose of confirming the distribution properties of

silane modification, the dispersion states of unmodified and

modified c-Fe2O3 are shown in Fig. 3b after 2 weeks.

Unmodified and silane-modified c-Fe2O3 were dispersed in

Fig. 1 XRD pattern of c-Fe2O3

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123

epoxy resin via ultrasonication and their stability was

observed after different times. The unmodified and silane-

modified c-Fe2O3 exhibited good dispersion initially after

ultrasonication, but the unmodified c-Fe2O3 started to settle

down gradually due to the agglomeration, whereas silane-

modified c-Fe2O3 exhibited good suspension stability after

two weeks. Therefore, as a result of surface coating and

increase of repulsive force among c-Fe2O3, the suspension

stability of nanoparticles in the resin is increased and com-

patibility between these two phases is improved. Figure 4a, b

illustrates the FT-IR spectrum of unmodified and modified c-

Fe2O3 nanoparticles. The absorption band at 586 cm-1 can

be assigned to Fe–O vibration mode and at 890 cm-1 and

790 cm-1 are due to the stretching of Fe–O–H and vibrations

of OH on the surface of c-Fe2O3 [22]. The hydroxyl groups

on the surface of c-Fe2O3 are also observed at 3,422 cm-1. In

the spectrum of modified c-Fe2O3 (Fig. 4b), a broad

absorption band in the range of 900–1,100 cm-1 is the

characteristic of Si–O and epoxide group-stretching vibra-

tions that confirm condensation reaction between methoxy

groups of GPTMS and hydroxyl groups of c-Fe2O3. The

absorption bands at 2,853 and 2,923 cm-1 are due to alkyl

groups [–(CH2)–] that are characteristic of organic coupling

agent [24, 25]. These results indicate the reaction of silane

Fig. 2 Particle size distribution of: (a) unmodified and (b) modified

c-Fe2O3

Fig. 3 (a) Chemical reaction

between magnetic c-Fe2O3 and

GPTMS, (b) dispersion of c-

Fe2O3 nanoparticles in epoxy

resin after 2 weeks (left:

unmodified c-Fe2O3, right:

modified c-Fe2O3)

J Mater Sci

123

molecules on the surface of c-Fe2O3 nanopowder. Figure 5

shows the TGA curves of unmodified and modified c-Fe2O3.

As can be seen in Fig. 5a, there is a total of 12 % weight loss

for pristine c-Fe2O3 started from *70 to 400 �C that is

mainly due to the loss of physically absorbed water and water

formed from condensation of hydroxyl groups on the surface

of nanoparticles [22]. Figure 5b shows that the weight of

modified c-Fe2O3 started to decrease from 70 to 250 �C

slowly which can be due to loss of moisture, and from 250 to

400 �C sharply which can be attributed to thermal decom-

position of the organic phase attached on the surface of

modified c-Fe2O3. Comparing TGA curves of unmodified

and modified c-Fe2O3, it is deduced that the maximum mass

fraction of organic phase (GPTES) on the surface of c-Fe2O3

is about 7 %.

Characterization of nanocomposites

DSC and TEM analysis

DSC technique has been extensively used to study the cure

reaction of epoxy resin [26, 27]. In this study, the curing

behavior of the neat epoxy, unmodified, and modified c-

Fe2O3/epoxy nanocomposites cured with stoichiometric

amount of TETA (based on DGEBA epoxide equivalent

weight) was examined by DSC. Figure 6 shows dynamic

DSC curves of modified c-Fe2O3/DGEBA/TETA mixtures.

The exothermic peak was characterized by noting the two

following parameters: Tp is temperature of the peak position,

and DHcure is the heat of cure reaction calculated by the

measurement of area under the exothermic peak. These

parameters and the Tg values obtained from the second DSC

scan are listed in Table 1. The Tp for DGEBA/TETA mix-

ture was observed at 100 �C which has shifted toward lower

temperatures for 1 and 5 wt% of c-Fe2O3 in DGEBA/TETA

mixture. The obtained values for DHcure and Tp indicate that

inclusion of c-Fe2O3 nanoparticles up to 5 wt% has catalytic

effect on the cure reaction of epoxy resin. Therefore, these

results indicate that large surface area of nanoparticles act as

catalyst up to a certain amount of 5 wt%, above that the c-

Fe2O3 particles agglomerate and block the cure reaction

between epoxide groups and TETA, thus the cure reaction

cannot be executed completely [28]. Because TETA was

Fig. 4 FT-IR spectrum of: (a) unmodified c-Fe2O3 and (b) modified

c-Fe2O3

Fig. 5 TGA curves of: (a) unmodified and (b) modified c-Fe2O3

Fig. 6 DSC curves of epoxy/TETA and modified c-Fe2O3/epoxy/

TETA systems at 10 �C min-1 and different contents of c-Fe2O3

Table 1 Curing characteristics of epoxy/TETA/c-Fe2O3 mixtures

c-Fe2O3

(wt %)

Tpa

(�C)

DHcure

(J/g)

Tg

(�C)

Pristine c-Fe2O3/epoxy

nanocomposite

0 100.2 -439.1 101

1 98.1 -459.5 106

5 93.4 -477.1 110

10 93.1 -425.9 104

Modified c-Fe2O3/epoxy

nanocomposite

1 95.4 -492.2 107

5 93.3 -524.1 113

10 93.1 -474.0 108

a Peak temperature

J Mater Sci

123

calculated based on the epoxide equivalent of DGEBA,

other reason for incomplete curing can be as a result of

insufficient amount of curing agent TETA to react with total

number of epoxide groups of DGEBA and 10 wt% epoxide-

terminated c-Fe2O3. Therefore, decrease in Tg value above

5 wt% of c-Fe2O3 can be due to the rise of segmental

movements which can be attributed to the formation of an

incomplete network. Similar behavior has also been reported

in other nanoparticle/epoxy systems [21, 29]. However, the

difference in the values of DHcure and Tg for modified and

unmodified c-Fe2O3/epoxy mixtures can be corroborated to

the better dispersion of modified c-Fe2O3 in the resin matrix,

and also due to contribution of epoxide groups of modified

c-Fe2O3 in the cure reaction.

TEM images of epoxy nanocomposites containing

1 wt% of modified c-Fe2O3 are shown in Fig. 7. The lower

magnification images in Fig. 7a give a general observation

of modified c-Fe2O3 dispersion into epoxy matrix. It can be

seen that modified c-Fe2O3 is homogenously dispersed

inside epoxy matrix, while some agglomeration is still

observed. The size of GPTMS-modified agglomerations is

about 100–300 nm. The size of agglomerations is estimated

to be larger for unmodified nanoparticles, because magnetic

nanoparticles strongly tend to aggregate due to large spe-

cific surface area, high surface energy, and magnetization.

The surface modification of c-Fe2O3 nanoparticles increa-

ses the steric hindrance between the nanoparticles and also

improves their compatibility in epoxy matrix. According to

high magnification images in Fig. 7b, the size of nanopar-

ticles is in the range of 17–20 nm (Fig. 7).

Magnetic properties

The magnetic properties of unmodified and modified c-

Fe2O3/epoxy nanocomposites were investigated using a

vibrating sample magnetometer (VSM). The graph pre-

sented in Fig. 8 represents the magnetization (M) (emu/g)

versus magnetic field (H) of the resulting nanocomposite

samples at room temperature. The coercivity and rema-

nence of the c-Fe2O3/epoxy nanocomposites tended to

zero as shown in Fig. 8, and, therefore, the superpara-

magnetic (SP) behavior of c-Fe2O3 nanocomposite is

confirmed. The saturation magnetization of nanocompos-

ites prepared from 5 wt% modified and unmodified

c-Fe2O3 was 1.06 emu/g and 0.59 emu/g, respectively, and

these values increased to 2.02 emu/g and 1.7 emu/g when

the content of modified and unmodified c-Fe2O3 was

increased to 10 wt%. Therefore, nanocomposites prepared

from surface-modified c-Fe2O3 showed higher saturation

magnetization than nanocomposites prepared from

unmodified c-Fe2O3 based on the same weight percent.

This can be due to the improved dispersion of modified

c-Fe2O3 in the resin matrix. It has been reported that

magnetic properties are influenced by powder size, surface

disorder, and distribution [30, 31]. Park et al. [32] also

reported that magnetic properties of Fe3O4/epoxy nano-

composites are influenced by dispersion pathway of mag-

netite nanoparticles due to silanization. However, Guo

et al. reported the nanoparticle surface functionalization

had little effect on the magnetic properties of vinyl ester

resin nanocomposites [33].

Fig. 7 TEM images at low

(a) and high (b) magnification

of modified c-Fe2O3/epoxy

nanocomposites

Fig. 8 Magnetic hysteresis loops of unmodified c-Fe2O3/epoxy

nanocomposites and modified c-Fe2O3/epoxy nanocomposites

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123

Mechanical properties of nanocomposites

Two types of mechanical tests, tensile and flexural, were

performed to evaluate the stiffness and strength of the

materials. The tensile stress–strain curve is a tool to provide

data on toughness, ultimate tensile strength, ultimate elon-

gation at break, and Young’s modulus. Stress–strain curves

for nanocomposite samples containing various contents of

unmodified and modified c-Fe2O3 are plotted in Fig. 9. The

results obtained from mechanical tests are summarized in

Table 2. As shown in Fig. 9a, by incorporation of 1 wt%

unmodified c-Fe2O3, the tensile strength of nanocomposite

increased marginally. However, further increment of loading

decreased the tensile strength of the nanocomposites in

comparison with the tensile strength of the pure resin, while

the Young’s modulus increased from 286.7 to 400.4 MPa

Fig. 9 Tensile curves of: (a) unmodified and (b) modified c-Fe2O3/

epoxy nanocomposites with different contents of c-Fe2O3

Table 2 Mechanical properties of c-Fe2O3 nanocomposites

c-Fe2O3

(wt %)

Tensile strength

(MPa) (STD)

Young’s modulus

(MPa) (STD)

Elongation at break

(%) (STD)

Flexural strength

(MPa) (STD)

Flexural modulus

(GPa) (STD)

Pristine c-Fe2O3

nanocomposite

0 54.4 (7.0) 286.7 (15.8) 3.9 (0.56) 98.9 (7.0) 2.9 (0.42)

1 56.4 (4.9) 332.0 (14.7) 3.3 (0.11) 96.7 (8.8) 3.7 (0.26)

5 53.7 (2.3) 400.4 (11.3) 2.6 (0.20) 91.3 (9.7) 4.0 (0.16)

10 52.4 (3.5) 421.9 (16.9) 2.5 (0.19) 89.3 (6.8) 3.6 (0.29)

Modified-c-Fe2O3

nanocomposite

1 60.7 (3.2) 404.6 (16.8) 3.7 (0.35) 104.4 (8.1) 4.1 (0.29)

5 63.3 (5.2) 430.7 (20.0) 2.9 (0.25) 109.5 (8.3) 4.4 (0.38)

10 65.3 (1.8) 509.8 (22.0) 2.7 (0.17) 117.6 (12.2) 4.6 (0.32)

STD standard deviation

Fig. 10 (a) Flexural strength and (b) flexural modulus of unmodified

and modified c-Fe2O3/epoxy nanocomposites

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123

when the content of unmodified c-Fe2O3 increased from 1 to

5 wt%. This increase is associated with the rigidity and

higher modulus of c-Fe2O3 nanoparticles. Therefore, it is

evident from the results that the cured material becomes

more brittle as the amount of unmodified c-Fe2O3 is

increased. Figure 9b shows the stress–strain curves for

nanocomposite samples containing various contents of

modified c-Fe2O3. As can be seen from the data listed in

Table 2, the mechanical properties of modified c-Fe2O3/

epoxy nanocomposites such as tensile strength and modulus

increased with increasing amount of modified c-Fe2O3 from

1 wt% up to 10 wt%. This increase was in the range of

12–20 % for tensile strength and 41–78 % for Young mod-

ulus, while the elongation at break reduced from 3.7 to

2.7 %. A similar behavior has also been observed in various

epoxy-based nanocomposites with other nanoscale particles

[34–39]. An explanation for these behaviors may be sug-

gested by considering the better size distribution and dis-

persibility of modified c-Fe2O3 in the resin matrix. The

quality of interface in composite usually plays an important

role in capability of materials to transfer stresses and elastic

deformation from matrix to fillers [37]. Therefore, another

important factor which has contributed in enhancement of

mechanical properties of modified c-Fe2O3/epoxy

Fig. 11 SEM micrographs of fractured surface of: (a) neat epoxy resin and nanocomposites with (b) 1 wt% modified c-Fe2O3, (c) 1 wt%

unmodified c-Fe2O3, (d) 10 wt% modified c-Fe2O3, and (e) 10 wt% unmodified c-Fe2O3

J Mater Sci

123

nanocomposites is formation of a strong interfacial adhesion

between inorganic and organic phases. This can be due to

formation of covalent bonds between epoxide groups of

modified c-Fe2O3 and epoxy/TETA system. It can be con-

cluded that as a result of homogeneous dispersion of modified

c-Fe2O3 and strong interfacial adhesion; the nanoparticles are

able to carry any part of external load. Figure 10a, b shows the

flexural strength and flexural modulus of unmodified and

modified c-Fe2O3/epoxy nanocomposites. As can be seen in

Fig. 10a and Table 2, the flexural strength and modulus of

nanocomposites increased with increasing the content of

modified c-Fe2O3 from 1 wt% up to 10 wt%. These results

are similar to the results of tensile test obtained for modified

c-Fe2O3/epoxy nanocomposites. However, the results

obtained for unmodified c-Fe2O3/epoxy nanocomposites are

slightly different. The flexural strength of nanocomposite

decreased (*10 %) with increasing amount of unmodified c-

Fe2O3. This may be due to insufficient dispersion stability and

formation of particle agglomeration.

Fracture surface morphology

SEM micrographs of fracture surfaces of neat epoxy and

unmodified and modified c-Fe2O3/epoxy nanocomposites are

shown with different enlargement factors in Fig. 11. As can

be seen in Fig. 11a, the neat epoxy shows a smooth fracture

surface as well as cracks in different planes after three-point

bending test. This is an indication of a brittle fracture of the

neat epoxy with lack of significant toughness mechanisms. It

indicates that a relatively small amount of energy was con-

sumed to fracture the specimens. Figure 11b, c shows the

SEM micrographs of fracture surface of epoxy nanocom-

posite containing 1 wt% modified and unmodified c-Fe2O3,

respectively. As can be seen in Fig. 11b, the fracture surface

of modified c-Fe2O3/epoxy nanocomposite shows rougher

features with elongated radial crack pattern. The fracture

morphology with elongated radial crack patterns corresponds

to a higher crack growth resistance of the composite [35].

Figure 11d, e shows the fracture surface of epoxy nano-

composite, with high magnification, containing 10 wt%

modified and unmodified c-Fe2O3, respectively. As can be

seen in the micrograph in Fig. 11d, it depicts rougher features

such as stress whitened zones and out-of-plane flaking

markings which normally exploit additional strain energy to

be formed during the deformation process of the specimens.

With increasing c-Fe2O3 content, more river line, debonding,

plastic void growth, and particle pull-out mechanisms can be

seen clearly. In modified c-Fe2O3/epoxy nanocomposites, the

particles are dispersed and distributed homogeneously within

the thermosetting matrix, leading to a rough surface acting as

obstacles for the propagating crack; subsequently, crack

deflection occurs [8]. The path of crack tip is distorted

because of bonded c-Fe2O3 nanoparticles making greater

resistance to crack propagation. However, the ductile-frac-

tured lines indicating a better interfacial bonding between the

modified c-Fe2O3 and epoxy resin matrix. There exist some

agglomerates at the fracture surface of unmodified c-Fe2O3/

epoxy nanocomposites, the large ones with the average size

of 100 lm can be seen in Fig. 11e. These agglomerations can

create microvoids at the fracture surface by particle pull-out

mechanism. When the crack reaches to the particle

agglomeration, the particles have to pull out of the polymer

matrix due to their poor bonding between the agglomerated

fillers and resin.

Thermal properties

The thermal stability of neat epoxy and unmodified and

modified c-Fe2O3/epoxy nanocomposites was examined by

TGA at a heating rate of 10 �C/min under a nitrogen

atmosphere. The results are presented in Fig. 12 and in

Table 3. The thermal stability factors, including the initial

decomposition temperature (TID), temperature of 5 %

weight loss (TD5), maximum weight-loss temperature

(Tmax), and char at 600 �C can be determined from the TGA

Fig. 12 TGA curves of: (a) neat epoxy and nanocomposite contain-

ing 10 wt% (b) unmodified c-Fe2O3, and (c) modified c-Fe2O3

Table 3 Thermal properties of neat epoxy and c-Fe2O3/epoxy

nanocomposites

System TIDa (�C) TD5

b (�C) Tmaxc (�C) Char yield (%)

Neat epoxy 352 353 385 13

10 wt% modified

c-Fe2O3/epoxy

341 330 363 21

10 wt% pristine

c-Fe2O3/epoxy

345 339 362 26

a Initial decomposition temperatureb 5 % weight-loss temperaturec Maximum weight-loss temperature

J Mater Sci

123

thermograms. The TD5 values of unmodified and modified

c-Fe2O3/epoxy nanocomposites were similar (*330 �C)

and lower than TD5 of neat epoxy (353 �C). The Tmax of

unmodified and modified c-Fe2O3/epoxy nanocomposites

(362 �C) is also lower than that of neat epoxy (385 �C).

This is probably due to catalytic effect of c-Fe2O3 nano-

particles on thermal degradation of organic phase [15].

Metallic compounds could serve as catalysts to degrade the

epoxy matrix, and the ability of c-Fe2O3 nanoparticles to

facilitate the thermal degradation of organic polymer net-

work at the initial stage might be attributed to this catalytic

effect. The char of unmodified and modified c-Fe2O3/epoxy

nanocomposites (26 and 21 % in Table 3 respectively) at

600 �C was higher than that of neat epoxy (13 %). The

lower char value of modified c-Fe2O3/epoxy nanocompos-

ite in comparison to that for unmodified c-Fe2O3/epoxy

nanocomposite can be due to thermal decomposition of

organic phase of the modified c-Fe2O3. This suggests that

the addition of unmodified and modified c-Fe2O3 has little

effect on the thermal stability of the epoxy resins.

Conclusions

In this study, nanocomposites of unmodified and surface

epoxide-terminated c-Fe2O3 were fabricated, characterized,

and their curing process and properties such as thermal,

mechanical, and magnetic were measured and compared with

the neat epoxy. The results showed that agglomeration of high

content (10 wt%) of unmodified c-Fe2O3 nanoparticles could

block the cure reaction between DGEBA and TETA and the

curing cannot be executed completely. As a result of this,

mechanical properties such as tensile and flexural strength, and

thermal stability and Tg of nanocomposite prepared with

10 wt% of unmodified c-Fe2O3 nanoparticles decreased.

Surface modification and epoxide functionalization ofc-Fe2O3

particles have improved their dispersion in the resin matrix and

increased interfacial adhesion between these two phases.

Therefore, epoxy nanocomposites prepared with modified c-

Fe2O3 exhibited enhanced Tg, and tensile and flexural strength.

The VSM results also revealed that saturation magnetization of

5 wt% modified c-Fe2O3/epoxy nanocomposites with super-

paramagnetic property was approximately 80 % greater than

that of unmodified c-Fe2O3/epoxy nanocomposites.

Acknowledgements The authors would like to thank Ms Maaso-

omeh Bazzar for her suggestion and fruitful comments during the

realization of this work.

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