Composites: Part B 66 (2014) 89–96

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Composites: Part B

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Mechanical properties of Fe3O4/GO/chitosan composites

http://dx.doi.org/10.1016/j.compositesb.2014.04.0341359-8368/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +82 312012565; fax: +82 312026693.E-mail address: rheeky@khu.ac.kr (K.Y. Rhee).

Mithilesh Yadav a, Kyong Yop Rhee a,⇑, Soo Jin Park b, David Hui c

a Department of Mechanical Engineering, College of Engineering, Kyung Hee University, Yongin 446-701, Republic of Koreab Department of Chemistry, Inha University, 253, Nam-gu, Incheon 402-751, Republic of Koreac Department of Mechanical Engineering, University of New Orleans, LA 70148, USA

a r t i c l e i n f o a b s t r a c t

Article history:Received 6 January 2014Received in revised form 10 April 2014Accepted 30 April 2014Available online 9 May 2014

Keywords:A. Polymer–matrix compositesB. Mechanical properties

A previously unreported iron oxide/graphene oxide/chitosan (Fe3O4/GO/CS) composite was prepared by asimple solution mixing-evaporation method. The structure, thermal stability, and mechanical propertiesof the composite were investigated by wide-angle X-ray diffraction, Fourier transform infrared spectros-copy, Raman spectroscopy, scanning electron microscopy, thermogravimetry analysis, and mechanicaltesting. The results obtained from these analyses revealed that chitosan, iron oxide and graphene oxidewere able to form a homogeneous mixture. A great synergistic effect of iron oxide platelets and grapheneoxide (GO) on reinforcing chitosan matrix has been observed. With incorporation of 0.5 wt.% Fe3O4 and1 wt.% GO, the tensile strength and Young’s modulus of the composite have significantly improved byabout 28% and 74%, respectively, compared with chitosan.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Chitosan (CS), the linear and partly acetylated (1–4)-2-amino-2-deoxy-b-D-glucan, is obtained from chitin and the second mostabundant natural polymer on earth [1,2]. It has been investigatedextensively over several decades for use in separation membranes,artificial skin, bone substitutes, and water treatment. It possesses anumber of interesting properties including biocompatibility, bio-degradability, and solubility in aqueous media [3–5]. Despite thenumerous advantages and unique properties of chitosan, its poormechanical and electrical properties restrict its use in a widerrange of applications. An effective approach for improving thephysical and mechanical properties of CS is to form organic–inor-ganic composites through incorporation of nanofillers, such asclays, metal nanoparticles, carbon nanotubes and graphene oxide[6–11].

Graphene, a single sheet of graphite, has an ideal 2D structurewith a monolayer of carbon atoms packed into a honeycomb crys-tal plane. Using both experimental and theoretical scientificresearch, researchers including Geim, Rao and Stankovich [12–14] have described the attractiveness of graphene in the materialsresearch field. Due to its sp2 hybrid carbon network as well asextraordinary mechanical, electronic, and thermal properties,graphene has opened new pathways for developing a wide rangeof novel functional materials. Perfect graphene does not exist

naturally, but bulk and solution processable functionalized graph-ene materials including graphene oxide (GO) can now be prepared[15–17]. The large surface area of GO has a number of functionalgroups, such as AOH, ACOOH, AOA, and C@O, which make GOhydrophilic and readily dispersible in water as well as someorganic solvents [18] , thereby providing a convenient access tofabrication of graphene-based materials by solution casting.According to several reports [19–21], GO can be dispersed through-out a selected polymer matrix to make GO-based composites withexcellent mechanical and thermal properties. Since GO is preparedfrom low-cost graphite, it has an outstanding price advantage overCNTs, which has encouraged studies of GO/synthetic polymer com-posites [22–24]. Many attempts have been made to improve thebiocompatibility and other activities of CS by fabrication of com-posites with metal oxide nanoparticles. Due to the magnetic natureof Fe3O4, these materials can be used to improve the delivery andrecovery of biomolecules for biosensing applications [25,26]. Inaddition, the nanoparticles have a unique ability to promote fastelectron transfer between an electrode and the active site of anenzyme, thus further improving their scope as biosensors. Effortshave been made to improve the electrical properties of CS for bio-sensor applications by the dispersion of superparamagnetic Fe3O4

nanoparticles [27]. The adsorption of CS onto Fe3O4 has beenreported to occur by an electrostatic attraction mechanism, makingChitosan an effective dispersant for the preparation of magneticsuspensions stabilized through electrostatic repulsive forces [28].GO–iron oxide nanoparticle (IONPs) composites have been synthe-sized by a number of groups and used for a variety of purposes

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[29–32]. In earlier work, Yang et al. [33] reported the use of GO–IONP as drug carriers. Chen et al. [34] demonstrated that the mag-netic GO–IONP composite could also be utilized as the T2-weightedmagnetic resonance (MR) contrast agent for in vitro cell labeling.The ability of CS to disperse Fe3O4 as well as GO and the facileadsorption of Fe3O4 by GO [35] enables CS to combine the mechan-ical and electrical properties of GO and Fe3O4 with the macropo-rous scaffold forming properties of CS. These Fe3O4/GO/CScomposites hold promise in providing a breakthrough platformtechnology for biosensing or bioenergetic applications [36]. Therehave been many reports on graphene oxide based chitosan com-posite with enhanced mechanical properties by simple physicalmixing of two components [37,38]. To the best of our knowledge,the synergistic effect of Fe3O4 and GO on the mechanical propertiesof chitosan composites has not been reported yet. Henceforth inthis study, in order to expand the various applications of CS, a sim-ple solution evaporation method was used to prepare novel Fe3O4/GO/CS composites. The three-component composites are expectedto have diverse properties because each component would contrib-ute different chemical and physical properties. The main objectiveof this study is to investigate the synergistic effect of Fe3O4 and GOon the material properties of Fe3O4/GO/CS composites.

2. Experimental method

2.1. Materials and methods

CS (average molecular weight = 350,000 gmol�1, 90% degree ofdeacetylation), potassium permanganate (analytical grade),sodium nitrate and graphite were purchased from Sigma Aldrich(Korea). Hydrogen peroxide was supplied by Daejung Chemicalsand Metals Company, Ltd. (South Korea). Hydrochloric acid waspurchased from Fluka. Sulfuric acid (98%) was purchased from Jun-sei Chemical Company (Japan). Magnetite (Fe3O4) nanopowder(<50 nm particle size (TEM), P98% trace metals basis) was pur-chased from Sigma Aldrich. Acetic acid was used to dissolve CSin distilled water. The water used was distilled and deionized.

2.2. Synthesis of graphene oxide

Graphene oxide (GO) was synthesized from natural graphiteflakes based on Hummers method [39]. Specifically, 2 g of graphiteand 1 g of NaNO3 were dissolved in 46 mL of concentrated H2SO4 inan ice bath. After about 15 min of stirring, 6 g of KMnO4 was grad-ually added into the suspension with stirring as slowly as possiblein order to control the reaction temperature below 20 �C. The sus-pension was stirred for 2 h and then maintained at 35 �C for30 min. Next, 92 mL of deionized water was slowly poured intothe suspension, resulting in a quick increase in temperature butwhich was controlled such that it remained less than 98 �C. After15 min, the suspension was further diluted to approximately280 mL with warm deionized water, after which 20 mL of 30%H2O2 was added to remove the residual KMnO4 and MnO2 tochange the color to luminous yellow. The resulting suspensionwas filtered and washed with warm 5% HCl aqueous solution anddeionized water, respectively, until no sulfates were detected,and the pH of the filtrate was adjusted to 7. The sample of GOwas dried under vacuum at 50 �C to a constant weight and thenmilled to an ideal particle size. The average size of graphene flakesare 500–5000 nm.

2.3. Preparation of Fe3O4/GO/CS composite films

Fe3O4/GO/CS composites were prepared by a simple solutionmixing-evaporation method. A CS solution of 2% (w/v) was

prepared by dissolving CS in a 2% (v/v) aqueous acetic acid solutionfollowed by filtration to remove the impurity. The iron oxide wasfirst swelled in 40 mL of distilled water and ultrasonicated for15 min. Then, the iron oxide suspension was added into the CSsolution with 0.5 wt.% iron oxide content with respect to CS, fol-lowed by stirring at 27 �C for 5 h. Subsequently, 1 wt.% GO suspen-sion was added into the mixture solution. The stirring rate waskept at a speed of 350 rpm for 1 h. The resulting CS concentrationin mixture solution was controlled to 1% (w/v) by evaporatingwater. The solutions were degassed for 30 min under vacuum.After that, Fe3O4/GO/CS solutions were poured into a Teflon moldand dried at 70 �C for 8 h to remove the solvents. The degassingand curing cycles were applied on the basis of trial and error.The dried membranes were soaked in 2 wt.% aqueous NaOH for1 h to remove the acid and washed with water to neutrality andthen dried at 70 �C for 6 h. The obtained composite film werepeeled from the glass plate and stored at room temperature. Meanthickness of the film was 0.04 mm.

2.4. Characterization

Wide-angle XRD patterns of Fe3O4/GO/CS composite films wererecorded with a Rigaku Rotaflex (RU-200B) X-ray diffractometerusing Cu Ka radiation with a Ni filter. The tube current and voltagewere 300 mA and 40 kV, respectively, and data from the 2h angularregions between 0 and 80 �C were collected. The thermal stabilityof the films was investigated using a TA instrument (SDT Q600)from 30 �C to 900 �C under a nitrogen atmosphere at a heating rateof 10 �C/min. Dynamic mechanical analysis (DMA) of compositeswas performed with a dynamic mechanical analyzer (DMA, Q800,TA Company) using tension membrane clamps at a frequency of1 Hz and a heating rate of 2 �C/min. Raman analysis of compositeswas carried out with a Jasco Raman spectrometer equipped with aCCD detector at a wavelength of 532 nm from 100 to 2000 cm�1 forsamples cut into 5 � 10 � 0.04 mm strips. The water contact anglesof the samples were measured using a FTA (FIRST TEN ANG-STROMS) 4000 (Search engine optimization, First Ten Angstroms,465 Dinwiddie Street, Portsmouth, Virginia 23704). The tensileproperties of Fe3O4/GO/CS composites films were measured atroom temperature with a universal test device (Instron 8871).The fracture surface morphology was analyzed by field emissionscanning electron microscopy (FE-SEM) (LEO SUPRA 55, Carl Zeiss,Germany).

3. Results and discussion

The hydrophilicity of the CS, GO/CS, Fe3O4/CS, Fe3O4/GO/CScomposites films were analyzed by measuring the contact anglesof a water droplet. As shown in Fig. 1, the Fe3O4/GO/CS compositesshows the highest contact angle among the tested compositesfilms and the contact angles of GO/CS composites is lower thanthat of CS. Higher contact angle value of a material means lowerhydrophilicity. Therefore, the hydrophilicity of the GO/CS compos-ites is higher than that of the CS due to the presence of a lot ofhydrophilic functional groups in GO. The hydrophilicity of theGO/CS composites can be controlled by adjusting the amount ofFe3O4 on the graphene oxide surface. Specifically, the averagedcontact angles of CS, GO/CS, Fe3O4/CS, Fe3O4/GO/CS compositeswere 80�, 78�, 72� and 81�, respectively.

Fig. 2 shows the XRD patterns of Fe3O4, CS, GO/CS, Fe3O4/CS, andFe3O4/GO/CS composites. XRD patterns for the Fe3O4 nanoparticlesdisplayed characteristic peaks (2h = 30.1�, 35.5�, 43.1�, 53.4�, 57.0�,and 62.6�). Patterns for Fe3O4/GO/CS composites revealed peaksindicative of pure Fe3O4 particles with a spinel structure. For CS,one major peak was observed at 2h = 20� (maximum intensity),

Fig. 1. Water contact angle of CS, GO/CS, Fe3O4/CS, Fe3O4/GO/CS composites.

Fig. 2. XRD patterns of Fe3O4, CS, GO/CS, Fe3O4/CS, and Fe3O4/GO/CS composites.

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which corresponded to the characteristic peak of CS chains alignedthrough intermolecular interactions [40]. Ogawa et al. [41] haveproposed three forms of CS, non-crystalline, hydrated crystalline,and anhydrous crystalline, with characteristic peaks ranging from10� to 20�. The broad peak around 2h = 14.2� corresponded to theanhydrous crystalline structure of CS [42]. This crystalline peakbecame more pronounced after incorporating the desired amountsof Fe3O4 and GO into CS. The peak at this angle being a broad peakmay indicate the presence of another polymorph, such as thehydrated crystalline structure, which exhibits a peak at2h = 11.7�. This result suggests an enhanced crystallinity or denserpacking in the main chain in comparison with neat CS.

The synergistic effect on the properties of CS by adding bothFe3O4 nanoparticles and GO was observed by FTIR and the resultis shown in Fig. 3. For the Fe3O4/CS and Fe3O4 nanoparticles, thepeaks at 592 cm�1 ascribe to FeAO group (Fig. 3d and a). In thespectrum of CS (Fig. 3b), the characteristic absorption bandsappeared at 1654.20 cm�1 ascribes to the amide I (C@O stretching),at 1588.49 cm�1 ascribes to amide II (NAH blending modes) and

Fig. 3. FT-IR spectra of Fe3O4, CS, GO/CS, Fe

the peak at 1420.66 cm�1 ascribes to ACAO stretching of primaryalcoholic group in CS. In the spectrum of Fe3O4/CS composites(Fig. 3d), compared with the spectrum of CS, the 1654.20 cm�1

peak of amide I, the 1588.49 cm�1 peak of amide II and the1420.66 cm�1 peak of ACAO stretching vibration of primary alco-holic group were shifted to 1648.38, 1562.73 cm�1 and 1411.41,respectively. The shifting of these peaks indicates that CS wascoated onto the magnetic Fe3O4 nanoparticles successfully.

3O4/CS, and Fe3O4/GO/CS composites.

Fig. 4. Raman spectrum of graphite, GO, GO/CS, Fe3O4/GO/CS composites.

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Fig. 3e shows that the amide I (1654.20 cm�1) and amide II(1588.49 cm�1) for Fe3O4/GO/CS are further shifted to higher fre-quency 1656.15 cm�1 and 1562.43 cm�1. Meanwhile, AOH groupband at 3393.10 cm�1 in CS is also shifted toward high frequency.

Fig. 5. TGA, DTG and DSC of graphite, GO, CS, G

This result indicates an enhanced hydrogen-bonding interactionbetween chitosan and the fillers by using both Fe3O4 and GO.

Fig. 4 shows the Raman spectroscopy of pristine graphite, GO,GO/CS, and Fe3O4/GO/CS composites. As shown in the figure, thepristine graphite showed three characteristic peaks at 1363.52(D-band, CAC), 1583.25 (G-band, C@C), and 2732.47 cm�1 (2D-band). The Raman spectrum of GO exhibited two prominent peaksat 1618.88 cm�1 and 1371.93 cm�1, corresponding to the well doc-umented G and D bands, respectively. The D band is due to defectsin the GO and staging disorder, while the G band is related to thegraphitic hexagon-pinch mode. In the present study, the ID/IG ratioof pristine graphite was 0.146, which indicated the graphite had anearly defect-free structure. It was found that GO had a muchhigher ID/IG ratio of 0.867, indicating the presence of defects. TheID/IG ratios for GO, GO/CS and Fe3O4/GO/CS composites were0.867, 0.897 and 0.894, respectively. Fe3O4/GO/CS has a higher ID/IG ratio than that of GO and GO/CS, which suggested that the struc-ture of Fe3O4/GO/CS composites was of the ordered carbon nano-sheet type. In addition, the intensities of the two peaks in GO/CSand Fe3O4/GO/CS composites were decreased, which was due tothe GO/CS and Fe3O4/GO/CS composites being less compact thanthe graphene oxide.

Thermogravimetric analysis (TGA) which was shown in Fig. 5confirmed that the pristine graphite was very stable and had noobservable weight loss when heated to 900 �C. According to this

O/CS, Fe3O4/CS, Fe3O4/GO/CS composites.

M. Yadav et al. / Composites: Part B 66 (2014) 89–96 93

result, GO was more thermally unstable than graphite, undergoinga three step degradation. GO lost 15% weight up to 176.67 �C. Theweight loss was possibly caused by the evaporation of adsorbedwater and thermal decompositions of oxygen-containing func-tional groups such as carboxyl, hydroxyl, epoxy, nitrogen dioxide,and ketone. The weight loss rate of GO increased with increasingtemperature from 176.67 �C to 250 �C and thereafter decreasedto attain a maximum value about 57.5 wt.% at about 587.60 �C,suggesting the presence of structural defects in GO caused bystrong acid oxidation. In comparing the thermograms of graphiteand GO (Fig. 5f and e), the integral procedural decomposition tem-perature (IPDT) [43] of graphite and GO (Table 1a) were 91826.36and 812.27, respectively, indicating that graphite is more ther-mally stable than GO. Thermogravimetric results, i.e., TGA, DTG,DSC curves of CS, GO/CS, Fe3O4/CS, and Fe3O4/GO/CS are shownin Fig. 5(d), (c), (b), (a) respectively. The 12 wt.% weight loss atabout 100 �C might have been due to loss of absorbed water, which

Table 1aThermal stabilities of the graphite and graphene oxide.

Precursor % W0 % Wf Ti Tf S1

Graphite 100.01 98.65 28.60 896.17 813.07Graphene Oxide 100.02 21.82 28.97 894.49 27673

Table 1bEffect of GO on the thermal stabilities of the composites studied.

Precursor % W0 % Wf PDT (�C) Tmax (�C) Ti Tf

CS 100.01 20.16 260.25 286.25 22.82 894.7GO/CS 100.01 28.27 250.00 288.50 24.85 894.6Fe3O4/CS 100.00 27.81 256.50 290.15 23.62 894.8Fe3O4/GO/CS 100.01 26.51 251.15 296.35 40.08 894.7

Fig. 6. Stress–strain curves (a), tensile strength (b), and elastic m

began at about 50 �C. The polymer decomposition temperature(PDT) was found to be 189.3 �C. The weight loss rate increased withincreasing temperature from 150 �C to 300 �C and thereafterdecreased to attain a maximum value of about 73.50 wt.% at900 �C. The degradation of Fe3O4/GO/CS composites occurred intwo steps at about 27.6–132.5 and 132.5–530 �C. The Tmax valueof this composites is 276.4 �C (in DTG, Fig. 5a). The IPDT and FDTof Fe3O4/GO/CS composites were 954.5 �C and 850 �C, respectively.Furthermore, the IPDT of chitosan, Fe3O4/CS and GO/CS were pre-sented in Table 1b. From this table, it is clear that GO/CS compos-ites are thermally more stable than CS and Fe3O4/CS. Again,comparing the thermograms of GO/CS and Fe3O4/GO/CS, the FDTand IPDT values were lower for Fe3O4/GO/CS, indicating thatFe3O4/GO/CS is less thermally stable than GO/CS.

Tensile strength and elastic modulus of CS, GO/CS, and Fe3O4/GO/CS composites were determined in order to investigate theeffect of adding Fe3O4 on the tensile properties of GO/CS

S2 S3 A� K� IPDT (�C)

85586.36 369.26 0.99 106.26 91826.36.59 18888.6 40004.24 0.54 1.68 812.27

S1 S2 S3 A� K� IPDT (�C)

1 20594.30 17570.82 49033.87 0.44 1.85 730.009 18658.13 24588.64 43744.98 0.49 2.32 1027.164 19310.00 24227.41 43585.79 0.49 2.25 1005.225 19357.16 23083.14 44638.71 0.49 2.19 954.45

odulus (c) of CS(p), GO/CS(q), Fe3O4/GO/CS(r) composites.

Fig. 7. Storage modulus (E0) and tand curves of GO/CS and Fe O /GO/CS composites.

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composites. Fig. 6a shows the tensile stress–strain curves for eachsample. For each case, the stress increased almost linearly withstrain in the early stages, with nonlinear behavior occurring beforethe maximum stress was reached. Fig. 6b compares the tensilestrengths of the CS, GO/CS and Fe3O4/GO/CS composites. The ten-sile strength of the Fe3O4/GO/CS composites was 10% and 28%higher than that of the GO/CS composites and CS, respectively.Fig. 6c compares the elastic modulus of the CS, GO/CS and Fe3O4/GO/CS composites. As shown in the figure, similar to the tensilestrength results, the elastic modulus improved with the additionof Fe3O4. Specifically, the elastic modulus of the Fe3O4/GO/CS com-posite was 22% and 74% higher than that of the GO/CS compositesand CS, respectively. These results clearly indicate that the tensilestrength and modulus of the GO/CS composites were improved byadding Fe3O4.

Dynamic mechanical analysis was performed on GO/CS andFe3O4/GO/CS composites to investigate the effect of Fe3O4 additionon the storage modulus and the glass transition temperature ofGO/CS composites. Variations of the storage modulus (E0) of GO/CS and Fe3O4/GO/CS composites films are shown in Fig. 7. TheFe3O4/GO/CS composites had a higher E0 than the GO/CS compos-ites, suggesting that the interactions between the CS matrix, GOand Fe3O4 were stronger. Retention ratio was defined as the stor-age modulus at 200 �C divided by the storage modulus at 50 �C.The retention ratios of GO/CS and Fe3O4/GO/CS were 0.548 and

3 4

Fig. 8. FESEM images of surfaces of CS (a) and the cross-sections of Fe3O4/GO/CS composites (b), and TEM image of Fe3O4/GO/CS composites (c).

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0.505, respectively, in which retention ratio was defined as thestorage modulus at 200 �C divided by the storage modulus at50 �C. This confirmed that Fe3O4/GO/CS composites possessedimproved mechanical properties at high temperature.

The glass transition temperatures (Tg) of GO/CS and Fe3O4/GO/CS composites were determined from the tand curves (Fig. 7).The Tg values of GO/CS and Fe3O4/GO/CS composites were deter-mined to be 267 �C and 264 �C, respectively. These results appearto contradict the tensile test results which were shown in Fig. 6,in which higher moduli correlate with higher Tg. This observedbehavior is termed antiplasticization which was defined as asimultaneous decrease in Tg with increased mechanical stiffeningand embrittlement caused by the addition of particular substancesto polymers [44]. Tensile results (Fig. 6) showed that the additionof Fe3O4 induced the embrittlement of the matrix (i.e., a decreasingtendency of ultimate elongation). These results are also in goodagreement with previous works using nanosized silica, silver, andaluminum that have shown antiplasticization leading to embrittle-ment of polymers [45]. The mechanism of antiplasticization is per-haps a combination of several factors: tight filling of the freevolume of the polymer molecules, interaction between the polargroups of the polymer and of the antiplasticizer, a physical stiffen-ing action due to the presence of rigid small molecules adjacent tothe polar groups of the polymer and consequently the restriction oflocal, noncooperative in-chain molecular motions [46]. Because themost flexible portions of a rigid condensation polymer are its polargroups (e.g., amino groups), the interaction of these groups withstiff and polar antiplasticizer molecules should reduce the flexibil-ity. It can be reasonably concluded that the mechanism of the tightfilling of the free volume of a polymer matrix and physical stiffen-ing due to the presence of rigid Fe3O4 nanoparticles may be thesole cause of the antiplasticization in this system. The tand peakheight was enhanced in the GO/CS composite compared with theFe3O4/GO/CS sample. The magnitude of the tand peak is relatedto the damping capability, or vibrational energy dissipation, whichreflects the toughness or stiffness of a material at the relaxationtemperature [47]. These results further corroborate the thermalstudy observations.

FESEM pictures of the fracture surfaces of CS and Fe3O4/GO/CScomposites after tensile testings are depicted in Fig. 8. As shownin Fig. 8a, the CS shows a smooth and tight fracture surface. Specif-ically, the fracture-surface images of Fe3O4/GO/CS films exhibited amaximum stack of sheets compared to CS due to the higher loadingof GO (Fig. 8b and c). A uniform distribution of Fe3O4 and GO wasobserved, with the ends of the broken GO on the fracture surface.The observation that most GO are broken rather than pulled outfrom the matrix indicates a strong interfacial adhesion betweenthe GO and CS matrix. Good dispersion and interfacial stress trans-fer are important factors for preparing reinforcing composites. TheTEM image of GO has been reported in the previous paper [48]. Asshown in the figure, the presence of thick black curly lines indi-cated that the sheets of GO had been dispersed homogeneouslyin the composites, and no aggregation of GO was observed.

4. Conclusion

We synthesized Fe3O4/GO/CS composites via a simple solutionmixing-evaporation method. FTIR result indicates an enhancedhydrogen-bonding interaction between CS and the fillers by usingboth Fe3O4 and GO. FESEM studies illustrated the excellent disper-sion of Fe3O4 and GO in the CS matrix, without aggregation. Inaddition, XRD analysis of Fe3O4/GO/CS nanocmposites showed thatthe GO sheets were well exfoliated in the CS matrix. TGA resultssuggested that graphite is more thermally stable than grapheneoxide and Fe3O4/GO/CS is less thermally stable than GO/CS

composites. The incorporation of 0.5 wt.% Fe3O4 increased the ten-sile strength and Young’s modulus of GO/CS by 28% and 74%,respectively.

Acknowledgements

This work was supported by the Basic Science Research Pro-gram through the National Research Foundation of Korea (NRF)funded by the Ministry of Education, Science and Technology (pro-ject number: 2013R1A1A2A10063466).

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